Rhombohedral phase Hf_(x)Zr_(1.x)O_(2)(HZO,x from 0 to 1)films are promising for achieving robust ferroelectric polarization without the need for an initial wake-up pre-cycling,as is normally the case for the more com...Rhombohedral phase Hf_(x)Zr_(1.x)O_(2)(HZO,x from 0 to 1)films are promising for achieving robust ferroelectric polarization without the need for an initial wake-up pre-cycling,as is normally the case for the more commonly studied orthorhombic phase.However,a large spontaneous polarization observed in rhombohedral films is not fully understood,and there are also large discrepancies between experimental and theoretical predictions.In this work,in rhombohedral ZrO_(2)thin films,we show that oxygen vacancies are not only a key factor for stabilizing the phase,but they are also a source of ferroelectric polarization in the films.This is shown experimentally through the investigation of the structural properties,chemical composition and the ferroelectric properties of the films before and after an annealing at moderate temperature(400℃)in an oxygen environment to reduce the V_(o)concentration compared.The experimental work is supported by density functional theory(DFT)calculations which show that the rhombohedral phase is the most stable one in highly oxygen defective ZrO_(2)films.The DFT calculations also show that V_(o)contribute to the ferroelectric polarization.Our findings reveal the importance of V_(o)for stabilizing rhombohedral ZrO_(2)thin films with superior ferroelectric properties.展开更多
Evidence for metallization in dense oxygen has been reported for over 30 years[Desgreniers et al.,J.Phys.Chem.94,1117(1990)]at a now routinely accessible 95 GPa[Shimizu et al.,Nature 393,767(1998)].However,despite the...Evidence for metallization in dense oxygen has been reported for over 30 years[Desgreniers et al.,J.Phys.Chem.94,1117(1990)]at a now routinely accessible 95 GPa[Shimizu et al.,Nature 393,767(1998)].However,despite the longevity of this result and the technological advances since,the nature of the metallic phase remains poorly constrained[Akahama et al.,Phys.Rev.Lett.74,4690(1995);Goncharov et al.,Phys.Rev.B 68,224108(2003);Ma,Phys.Rev.B 76,064101(2007);and Weck et al.,Phys.Rev.Lett.102,255503(2009)].In this work,through Raman spectroscopy,we report the distinct vibrational characteristics of metallicζ-O_(2) from 85 to 225 GPa.In comparison with numerical simulations,wefind reasonable agreement with the candidate structure up to about 150 GPa.At higher pressures,the C2/mstructure is found to be unstable and incompatible with experimental observations.Alternative candidate structures,and Ci,with C2/m C2/conly two molecules in the primitive unit cell,are found to be stable and more compatible with measurements above 175 GPa,indicative of the dissociation of(O_(2))4 units.Further,we report and discuss a strong hysteresis and metastability with the precursory phaseϵ-O_(2).Thesefindings will reinvigorate experimental and theoretical work into the dense oxygen system,which will have importance for oxygen-bearing chemistry,prevalent in the deep Earth,as well as fundamental physics.展开更多
Sulfur and lanthanum hydrides under compression display superconducting states with high observed critical temperatures.It has been recently demonstrated that carbonaceous sulfur hydride displays room temperature supe...Sulfur and lanthanum hydrides under compression display superconducting states with high observed critical temperatures.It has been recently demonstrated that carbonaceous sulfur hydride displays room temperature superconductivity.However,this phenomenon has been observed only at very high pressure.Here,we theoretically search for superconductors with very high critical temperatures,but at much lower pressures.We describe two of such sodalite-type clathrate hydrides,YbH6 and LuH6.These hydrides are metastable and are predicted to superconduct with T_(c)~145 K at 70 GPa and T_(c)~273 K at 100 GPa,respectively.This striking result is a consequence of the strong interrelationship between the f states present at the Fermi level,structural stability,and the final T_(c) value.For example,TmH6,with unfilled 4f orbitals,is stable at 50 GPa,but has a relatively low value of T_(c) of 25 K.The YbH6 and LuH6 compounds,with their filled f-shells,exhibit prominent phonon"softening",which leads to a strong electron-phonon coupling,and as a result,an increase in T_(c).展开更多
A conduction channel model is proposed to explain the high conductivity property of nc-Si: H. Detailed energy band diagram is developed based on the analysis and calculation, and the conductivity of the nc-Si: H was t...A conduction channel model is proposed to explain the high conductivity property of nc-Si: H. Detailed energy band diagram is developed based on the analysis and calculation, and the conductivity of the nc-Si: H was then analysed on the basis of energy band theory. It is assumed that the conductivity of the nc-Si: H stems from two parts: the conductance of the interface, where the transport mechanism is identified as a thermal-assisted tunnelling process, and the conductance along the channel around the grain, which mainly determined the high conductivity of the nc -Si: H. The conductivity of nc - Si: H is calculated and compared with the experiment data. The theory is in agreement with the experiment.展开更多
In the period 2003-2011, lightning over-voltages accounted for about 47% of the total number of distribution transformer failures observed in the service area ofAES Sul, a power company that operates in the state of R...In the period 2003-2011, lightning over-voltages accounted for about 47% of the total number of distribution transformer failures observed in the service area ofAES Sul, a power company that operates in the state of Rio Grande doSul, in South Brazil. This paper presents the results of an investigation on the influence of the distance between transformer and MV arresters on the surges at the transformer windings caused by direct strikes to the MV network. The analysis, performed through simulations using the Alternative Transients Program, shows that in general higher voltages are produced by subsequent strokes. Although in relation to the primary side the surges transferred to the secondary are much less affected by the distance between transformers and primary arresters, such distance should always be kept as short as possible in order to reduce the probability of occurrence of transformer failures due to over-voltages at the MV bushings.展开更多
Defined as total productive maintenance carried out by all cooperators in Supply Chain, Total Operational Maintenance (TOM) focuses on adapting to collaborative business environment in virtue of Internet & Intrane...Defined as total productive maintenance carried out by all cooperators in Supply Chain, Total Operational Maintenance (TOM) focuses on adapting to collaborative business environment in virtue of Internet & Intranet. It focuses on the managerial ideology of embedded with Quick Response (QR),Total Productive Maintenance (TPM) and Supply Chain. And the theoretical architecture and implementation is also described. It offers emphatically that it is necessary to exceed competitive advantage of the enterprises by optimizing reliability, empowerment and Overall Facilities Effectiveness (OFE) applying TOM together into the strategic improvement plan.展开更多
The mid-T_(C) superconductor Ba1-XKXBiO3(BKBO)exhibits different superconducting mechanisms depending on x,in the range∼0.35–0.65.The optimal doping for the highest T_(C) is reported to be around x=0.4.To understand...The mid-T_(C) superconductor Ba1-XKXBiO3(BKBO)exhibits different superconducting mechanisms depending on x,in the range∼0.35–0.65.The optimal doping for the highest T_(C) is reported to be around x=0.4.To understand more about the dependence of the superconducting mechanism on x,high quality and reproducible epitaxial films with controlled x are needed.This has been challenging owing to the volatility of K and(to a lesser extent)Bi.In this work,we use pulsed laser deposition(PLD)with several novel process steps to achieve high-quality films in a reproducible way.These include a modified method for target preparation,a low NO_(2) growth pressure,and precise positioning of substrates in the PLD plume.Optimum T_(C) films(32 K onset)were grown from an x=0.4 target,i.e.with no excess K,as is normally used.Stable,higher K content films(made from an x=0.45 target),were also grown.These x=0.45 films had a lower T_(C) (22.5 K onset),as expected for(K)overdoped films,with very high upper critical field,H_(C2) (0 K),and irreversibility field,Hirr(0 K),values,from linear extrapolation,of∼31.7 T and∼28.8 T,respectively.The growth methodology demonstrated in this work is highly beneficial for fundamental mechanistic studies of this complex superconductor on which there is renewed interest,and where controlled compositions and crystalline quality are currently limited.展开更多
Using lower-cost lasers, 30% savings are possible for 10-Gb/s uncompensated metro transmission over NZDF, compared to G.652 fiber. We present WDM transmission results for a mixed plant of NZDF rings interconnected to ...Using lower-cost lasers, 30% savings are possible for 10-Gb/s uncompensated metro transmission over NZDF, compared to G.652 fiber. We present WDM transmission results for a mixed plant of NZDF rings interconnected to G.652.C-fiber access laterals.展开更多
Dispersion compensation with few-mode fibers is emerging as a promising technique that can provide full dispersion and dispersion-slope compensation. The inherent modal path diversity of these fibers allows implementa...Dispersion compensation with few-mode fibers is emerging as a promising technique that can provide full dispersion and dispersion-slope compensation. The inherent modal path diversity of these fibers allows implementation of static as well as tunable dispersion management schemes. In addition, the low non-linearity of this technology can improve system OSNR, leading to enhancements in transmission distances.展开更多
We discuss the concept of coarse wavelength-division multiplexing (CWDM) for metro networks. After reviewing the requirements on components such as lasers and fiber, we propose different architectures for a flexible u...We discuss the concept of coarse wavelength-division multiplexing (CWDM) for metro networks. After reviewing the requirements on components such as lasers and fiber, we propose different architectures for a flexible upgrade of existing CWDM systems.展开更多
This paper reviews the recent advances in multi-terabit long-haul transmission technologies for terrestrial optical networks. The use of high performance new fibres, low-noise Raman amplification, optimised modulation...This paper reviews the recent advances in multi-terabit long-haul transmission technologies for terrestrial optical networks. The use of high performance new fibres, low-noise Raman amplification, optimised modulation formats, and forward error correction is shown to be effective for capacity and distance expansion.展开更多
We compare different discreted DCF Raman amplifier configurations, including single-stage and dual-stage. The optimum design with respect to SNR degradation, compromise linear and nonlinear impairments.
Tran smissio n electro n microscopes (TEM) are widely used in nan otech no logy research. However, it is still challe nging to characterize nano scale objects;their small size coupled with dynamical diffraction makes ...Tran smissio n electro n microscopes (TEM) are widely used in nan otech no logy research. However, it is still challe nging to characterize nano scale objects;their small size coupled with dynamical diffraction makes interpret!ng real- or reciprocal-space data difficult. Scanning precession electron diffraction ((S)PED) represents an invaluable contribution, reducing the dynamical contributions to the diffraction pattern at high spatial resolution. Here a detailed analysis of wurtzite InP nanowires (30-40 nm in diameter) containing a screw dislocation and an associated wire lattice torsion is presented. It has been possible to characterize the dislocation with great detail (Burgers and line vector, handedness). Through careful measurement of the strain field and comparison with dynamical electron diffraction simulations, this was found to be compatible with a Burgers vector modulus equal to one hexagonal lattice cell parameter despite the observed crystal rotation rate being larger (ca. 20%) than that predicted by classical elastic theory for the nominal wire diameter. These findings corroborate the importance of the (S)PED technique for characterizing nano scale materials.展开更多
基金supported by the Portuguese Foundation for Science and Technology(FCT)in the framework of the Strategic Funding Contract UIDB/04650/2020 and by M-ERA.NET NanOx4EStor Contract no.M-ERA-NET3/0003/2021the Oblivion Supercomputer at university ofévora,funded by the ENGAGE SKA Research Infrastructure(reference POCI-01-0145-FEDER022217-COMPETE 2020 and FCT)+4 种基金by the BigData@UE project(reference ALT20-03-0246-FEDER-000033-FEDER and the Alentejo 2020 Regional Operational Program),for providing HPC resources in the framework of the advanced computing project CPCA/A1/415075/2021 awarded by FCT IPthe financial support through the contract FEDR-POC No.332/390008/29.122020-SMIS 109522the CERIC-ERIC Consortium for access to experimental facilities and financial support under proposals 20202037,20202038 and 20192055supported by the COST Action CA20116-European Network for Innovative and Advanced Epitaxy(OPERA)the Royal Academy of Engineering grant,CIET1819_24,for funding and the ERC grant,EU-H2020-ERC-ADG#882929,EROS
文摘Rhombohedral phase Hf_(x)Zr_(1.x)O_(2)(HZO,x from 0 to 1)films are promising for achieving robust ferroelectric polarization without the need for an initial wake-up pre-cycling,as is normally the case for the more commonly studied orthorhombic phase.However,a large spontaneous polarization observed in rhombohedral films is not fully understood,and there are also large discrepancies between experimental and theoretical predictions.In this work,in rhombohedral ZrO_(2)thin films,we show that oxygen vacancies are not only a key factor for stabilizing the phase,but they are also a source of ferroelectric polarization in the films.This is shown experimentally through the investigation of the structural properties,chemical composition and the ferroelectric properties of the films before and after an annealing at moderate temperature(400℃)in an oxygen environment to reduce the V_(o)concentration compared.The experimental work is supported by density functional theory(DFT)calculations which show that the rhombohedral phase is the most stable one in highly oxygen defective ZrO_(2)films.The DFT calculations also show that V_(o)contribute to the ferroelectric polarization.Our findings reveal the importance of V_(o)for stabilizing rhombohedral ZrO_(2)thin films with superior ferroelectric properties.
基金The computational resources were provided by the Cambridge Tier-2 sys-tem operated by the University of Cambridge Research Computing Service and funded by the UK EPSRC(Grant No.EP/P020259/1).
文摘Evidence for metallization in dense oxygen has been reported for over 30 years[Desgreniers et al.,J.Phys.Chem.94,1117(1990)]at a now routinely accessible 95 GPa[Shimizu et al.,Nature 393,767(1998)].However,despite the longevity of this result and the technological advances since,the nature of the metallic phase remains poorly constrained[Akahama et al.,Phys.Rev.Lett.74,4690(1995);Goncharov et al.,Phys.Rev.B 68,224108(2003);Ma,Phys.Rev.B 76,064101(2007);and Weck et al.,Phys.Rev.Lett.102,255503(2009)].In this work,through Raman spectroscopy,we report the distinct vibrational characteristics of metallicζ-O_(2) from 85 to 225 GPa.In comparison with numerical simulations,wefind reasonable agreement with the candidate structure up to about 150 GPa.At higher pressures,the C2/mstructure is found to be unstable and incompatible with experimental observations.Alternative candidate structures,and Ci,with C2/m C2/conly two molecules in the primitive unit cell,are found to be stable and more compatible with measurements above 175 GPa,indicative of the dissociation of(O_(2))4 units.Further,we report and discuss a strong hysteresis and metastability with the precursory phaseϵ-O_(2).Thesefindings will reinvigorate experimental and theoretical work into the dense oxygen system,which will have importance for oxygen-bearing chemistry,prevalent in the deep Earth,as well as fundamental physics.
基金Supported by the National Natural Science Foundation of China(Grant Nos.12122405,51632002,and 11974133)the Program for Changjiang Scholars and Innovative Research Team in Universities(Grant No.IRT 15R23)+1 种基金financial support from the Engineering and Physical Sciences Research Council(Grant No.EP/P022596/1)。
文摘Sulfur and lanthanum hydrides under compression display superconducting states with high observed critical temperatures.It has been recently demonstrated that carbonaceous sulfur hydride displays room temperature superconductivity.However,this phenomenon has been observed only at very high pressure.Here,we theoretically search for superconductors with very high critical temperatures,but at much lower pressures.We describe two of such sodalite-type clathrate hydrides,YbH6 and LuH6.These hydrides are metastable and are predicted to superconduct with T_(c)~145 K at 70 GPa and T_(c)~273 K at 100 GPa,respectively.This striking result is a consequence of the strong interrelationship between the f states present at the Fermi level,structural stability,and the final T_(c) value.For example,TmH6,with unfilled 4f orbitals,is stable at 50 GPa,but has a relatively low value of T_(c) of 25 K.The YbH6 and LuH6 compounds,with their filled f-shells,exhibit prominent phonon"softening",which leads to a strong electron-phonon coupling,and as a result,an increase in T_(c).
基金he Natural Science Foundation of Hubei Province of China!96J026
文摘A conduction channel model is proposed to explain the high conductivity property of nc-Si: H. Detailed energy band diagram is developed based on the analysis and calculation, and the conductivity of the nc-Si: H was then analysed on the basis of energy band theory. It is assumed that the conductivity of the nc-Si: H stems from two parts: the conductance of the interface, where the transport mechanism is identified as a thermal-assisted tunnelling process, and the conductance along the channel around the grain, which mainly determined the high conductivity of the nc -Si: H. The conductivity of nc - Si: H is calculated and compared with the experiment data. The theory is in agreement with the experiment.
文摘In the period 2003-2011, lightning over-voltages accounted for about 47% of the total number of distribution transformer failures observed in the service area ofAES Sul, a power company that operates in the state of Rio Grande doSul, in South Brazil. This paper presents the results of an investigation on the influence of the distance between transformer and MV arresters on the surges at the transformer windings caused by direct strikes to the MV network. The analysis, performed through simulations using the Alternative Transients Program, shows that in general higher voltages are produced by subsequent strokes. Although in relation to the primary side the surges transferred to the secondary are much less affected by the distance between transformers and primary arresters, such distance should always be kept as short as possible in order to reduce the probability of occurrence of transformer failures due to over-voltages at the MV bushings.
文摘Defined as total productive maintenance carried out by all cooperators in Supply Chain, Total Operational Maintenance (TOM) focuses on adapting to collaborative business environment in virtue of Internet & Intranet. It focuses on the managerial ideology of embedded with Quick Response (QR),Total Productive Maintenance (TPM) and Supply Chain. And the theoretical architecture and implementation is also described. It offers emphatically that it is necessary to exceed competitive advantage of the enterprises by optimizing reliability, empowerment and Overall Facilities Effectiveness (OFE) applying TOM together into the strategic improvement plan.
基金All the authors thank the ONRG-NICOP-N62909-18-1-2092 grant for funding this researchMuireann de h-Óra also thanks European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement number 861145–BeMAGIC for financial supportJudith L.MacManus-Driscoll also thanks the Royal Academy of Engineering Chair in Emerging Technologies grant-CIET1819\24 and the ERC grant EU-H2020-ERC-ADG#882929 EROS.
文摘The mid-T_(C) superconductor Ba1-XKXBiO3(BKBO)exhibits different superconducting mechanisms depending on x,in the range∼0.35–0.65.The optimal doping for the highest T_(C) is reported to be around x=0.4.To understand more about the dependence of the superconducting mechanism on x,high quality and reproducible epitaxial films with controlled x are needed.This has been challenging owing to the volatility of K and(to a lesser extent)Bi.In this work,we use pulsed laser deposition(PLD)with several novel process steps to achieve high-quality films in a reproducible way.These include a modified method for target preparation,a low NO_(2) growth pressure,and precise positioning of substrates in the PLD plume.Optimum T_(C) films(32 K onset)were grown from an x=0.4 target,i.e.with no excess K,as is normally used.Stable,higher K content films(made from an x=0.45 target),were also grown.These x=0.45 films had a lower T_(C) (22.5 K onset),as expected for(K)overdoped films,with very high upper critical field,H_(C2) (0 K),and irreversibility field,Hirr(0 K),values,from linear extrapolation,of∼31.7 T and∼28.8 T,respectively.The growth methodology demonstrated in this work is highly beneficial for fundamental mechanistic studies of this complex superconductor on which there is renewed interest,and where controlled compositions and crystalline quality are currently limited.
文摘Using lower-cost lasers, 30% savings are possible for 10-Gb/s uncompensated metro transmission over NZDF, compared to G.652 fiber. We present WDM transmission results for a mixed plant of NZDF rings interconnected to G.652.C-fiber access laterals.
文摘Dispersion compensation with few-mode fibers is emerging as a promising technique that can provide full dispersion and dispersion-slope compensation. The inherent modal path diversity of these fibers allows implementation of static as well as tunable dispersion management schemes. In addition, the low non-linearity of this technology can improve system OSNR, leading to enhancements in transmission distances.
文摘We discuss the concept of coarse wavelength-division multiplexing (CWDM) for metro networks. After reviewing the requirements on components such as lasers and fiber, we propose different architectures for a flexible upgrade of existing CWDM systems.
文摘This paper reviews the recent advances in multi-terabit long-haul transmission technologies for terrestrial optical networks. The use of high performance new fibres, low-noise Raman amplification, optimised modulation formats, and forward error correction is shown to be effective for capacity and distance expansion.
文摘We compare different discreted DCF Raman amplifier configurations, including single-stage and dual-stage. The optimum design with respect to SNR degradation, compromise linear and nonlinear impairments.
文摘Tran smissio n electro n microscopes (TEM) are widely used in nan otech no logy research. However, it is still challe nging to characterize nano scale objects;their small size coupled with dynamical diffraction makes interpret!ng real- or reciprocal-space data difficult. Scanning precession electron diffraction ((S)PED) represents an invaluable contribution, reducing the dynamical contributions to the diffraction pattern at high spatial resolution. Here a detailed analysis of wurtzite InP nanowires (30-40 nm in diameter) containing a screw dislocation and an associated wire lattice torsion is presented. It has been possible to characterize the dislocation with great detail (Burgers and line vector, handedness). Through careful measurement of the strain field and comparison with dynamical electron diffraction simulations, this was found to be compatible with a Burgers vector modulus equal to one hexagonal lattice cell parameter despite the observed crystal rotation rate being larger (ca. 20%) than that predicted by classical elastic theory for the nominal wire diameter. These findings corroborate the importance of the (S)PED technique for characterizing nano scale materials.
