The article presents an experimental study on the flow of an eutectic gallium alloy in a cylindrical cell,which is placed in an alternating magnetic field.The magnetic field is generated by a coil connected to an alte...The article presents an experimental study on the flow of an eutectic gallium alloy in a cylindrical cell,which is placed in an alternating magnetic field.The magnetic field is generated by a coil connected to an alternating current source.The coil is located at a fixed height in such a way that its plane is perpendicular to the gravity vector,which in turn is parallel to the axis of the cylinder.The position of the cylinder can vary in height with respect to the coil.The forced flow of the considered electrically conductive liquid is generated due to the action of the localized electromagnetic force.It is assumed that under the action of the alternating magnetic field,the liquid is heated uniformly,and the resulting heat is quickly absorbed by the forced flow,so that liquid free convection can be neglected.The experiment is carried out using an ultrasonic Doppler anemometer.One transducer is installed in the axially located cylinder sluice and the other transducer is placed in the near-wall region.According to the results,a velocity profile,corresponding to a two-tori flow pattern can be hardly obtained in the low frequency range of the power supply.However,this is possible in the high frequency range.The average velocity profiles depend essentially on the location of the coil relative to the cell.The spectral analysis of velocity signals shows that the amplitude of the velocity pulsations is comparable to the average value of the flow velocity.Such experimental results and their verification through comparison with numerical calculations are intended to support the development of new methods for reducing the intensity of vortex flows during the electromagnetic separation of impurities through an electromagnetic induction mechanism(able to produce an electromotive force that displaces particles).展开更多
CONSPECTUS:Efficient photovoltaics(PV)require capturing and converting solar energy across a broad range of energy.Losses due to thermalization and sub-bandgap photons place,however,significant boundaries on the perfo...CONSPECTUS:Efficient photovoltaics(PV)require capturing and converting solar energy across a broad range of energy.Losses due to thermalization and sub-bandgap photons place,however,significant boundaries on the performance of solar cells.For conventional singlejunction cells,the theoretical maximum power conversion efficiency is capped at 33%,a constraint known as the detailed balance limit.Realizing the full potential of PVs requires developing novel strategies to overcome this fundamental obstacle.This Account describes the photon-management capabilities of acenes and addresses these fundamental losses enroute toward enhancing PV performances.For high-energy photons that exceed the semiconductor’s bandgap energy,singlet fission(SF)is a down-conversion pathway to mitigate thermalization losses.SF is a process in organic materials,in which a singlet excited state is split into two independent triplet excited states,effectively doubling the number of charge carriers.Pentacenes stand out among acenes due to their exergonic nature of SF.Numerous molecular pentacene dimers have been synthesized to elucidate the relationship between structure and enhancing SF efficiency.A broader light-harvesting range of SF materials is realized by covalently attaching complementary absorbing energy donors to set up energy donor−acceptor conjugates.Förster resonance energy transfer(FRET)is operative in these energy donor-acceptor conjugates,effectively extending the absorption of SF materials,as the energy donor efficiently transfers its absorbed excitation energy to the energy acceptor.Our studies on various binding motifs show that FRET efficiency depends not only on parameters like the energy donor−acceptor distance and spectral overlap but also on subtle factors such as the alignment of transition dipoles,which significantly affect the energy transfer dynamics and efficiency.Turning to low-energy photons,triplet−triplet annihilation up-conversion(TTA-UC)provides a means of light up-conversion and,thereby,the reduction of sub-bandgap losses.In TTA-UC,a singlet excited state that is potent enough to generate charge carriers is formed by combining two triplet excitons.It is effectively the reverse process of SF.The higher triplet energy of tetracene and an endergonic SF renders them highly effective for TTA-UC.We focus on various tetracene-based systems that maximize TTA-UC efficiency.Besides TTA-UC,two-photon absorption(TPA)is yet another mechanism to leverage below-bandgap photons.It is a nonlinear optical(NLO)process,and acenes reveal NLO properties that are essential for extending light absorption into the near-infrared and still powering SF.We demonstrate in our proof-of-concept studies how TPA further broadens the application potential of acenes for PV systems.The strategies outlined in this Account illustrate that acenes are valuable for addressing mechanistic losses in conventional solar cells.In the final section,we examine light storage following SF by means of interfacial electron transfer.Efficient charge-injection powered by SF materials still requires more research before being implemented in large-scale PV designs.Overall,the advances discussed in this Account not only highlight the pivotal role of acenes as model systems to investigate photon down-and up-conversion processes but also paint a promising picture that more efficient solar energy conversion schemes exceeding the detailed-balance limit can be realized by implementing these materials.展开更多
Millions of patients and their caretakers live and deal with the devastating consequences of spinal cord injury(SCI)worldwide.Despite outstanding advances in the field to both understand and tackle these pathologies,a...Millions of patients and their caretakers live and deal with the devastating consequences of spinal cord injury(SCI)worldwide.Despite outstanding advances in the field to both understand and tackle these pathologies,a cure for SCI patients,with their peculiar characteristics,is still a mirage.One of the most promising therapeutic strategies to date for these patients involves the use of epidural electrical stimulation.In this context,electrically active materials such as graphene and its derivates become particularly interesting.Indeed,solid evidence of their capacity to closely interact with neural cells and networks is growing.Encouraged by previous findings in our laboratory on the exploration of 3D porous reduced graphene oxide(rGO)scaffolds in chronic cervical hemisected rats(C6),herein we report their neuro-reparative properties when chronically implanted in complete transected rats(T9-T10),in which no preserved contralateral neural networks can assist in any observed recovery.Electrophysiological recordings from brainstem regions show antidromic activation of a small population of neurons in response to electrical stimulation caudal to the injury.These neurons are located in the Gigantocellular nucleus of reticular formation and vestibular nuclei,both regions directly related to motor functions.Together with histological features at the lesion site,such as more abundant and larger blood vessels and more abundant,longer and more homogeneously distributed axons,our results corroborate that rGO scaffolds create a permissive environment that allows the invasion of functional axonic processes from neurons located in brainstem nuclei with motor function in a rat model of complete thoracic transection.Additionally,behavioral tests evidence that these scaffolds play an important role in whole-body mechanical stabilization(postural control)proved by the absence of scoliosis,a higher trunk stability and a larger cervico-thoraco-lumbar movement range in rGO-implanted rats.展开更多
Here,we propose a method to determine the thickness of the most common transition metal dichalcogenides (TMDCs) placed on the surface of transparent stamps,used for the deterministic placement of two-dimensional mater...Here,we propose a method to determine the thickness of the most common transition metal dichalcogenides (TMDCs) placed on the surface of transparent stamps,used for the deterministic placement of two-dimensional materials,by analyzing the red,green and blue channels of transmission-mode optical microscopy images of the samples.In particular,the blue channel transmittance shows a large and monotonic thickness dependence,making it a very convenient probe of the flake thickness.The method proves to be robust given the small flake-to-flake variation and the insensitivity to doping changes of MoS2.We also tested the method for MoSe2,WS2 and WSe2.These results provide a reference guide to identify the number of layers of this family of materials on transparent substrates only using optical microscopy.展开更多
This paper considers the problem of natural vibrations of a deformable structure containing elements made of piezomaterials.The piezoelectric elements are connected through electrodes to an external electric circuit,w...This paper considers the problem of natural vibrations of a deformable structure containing elements made of piezomaterials.The piezoelectric elements are connected through electrodes to an external electric circuit,which consists of resistive,inductive and capacitive elements.Based on the solution of this problem,the parameters of external electric circuits are searched for to allow optimal passive control of the structural vibrations.The solution to the problem is complex natural vibration frequencies,the real part of which corresponds to the circular eigenfrequency of vibrations and the imaginary part corresponds to its damping rate(damping ratio).The analysis of behaviour of the imaginary parts of complex eigenfrequencies in the space of external circuit parameters allows one to damp given modes of structure vibrations.The effectiveness of the proposed approach is demonstrated using a cantilever-clamped plate and a shell structure in the form of a semi-cylinder connected to series resonant RL circuits.展开更多
A well-established strategy to synthesize heterogeneous,metal-organic framework(MOF)catalysts that exhibit nanoconfinement effects,and specific pores with highly-localized catalytic sites,is to use organic linkers con...A well-established strategy to synthesize heterogeneous,metal-organic framework(MOF)catalysts that exhibit nanoconfinement effects,and specific pores with highly-localized catalytic sites,is to use organic linkers containing organocatalytic centers.Here,we report that by combining this linker approach with reticular chemistry,and exploiting three-dimensioanl(3D)MOF-structural data from the Cambridge Structural Database,we have designed four heterogeneous MOF-based catalysts for standard organic transformations.These programmable MOFs are isoreticular versions of pcu IRMOF-16,feu UiO-68 and pillared-pcu SNU-8X,the three most common topologies of MOFs built from the organic linker p.p'-terphenyldicarboxylic acid(tpdc).To synthesize the four squaramide-based MOFs,we designed and synthesized a linker,4,4’-((3,4-dioxocyclobut-1-ene-1,2-diyl)bis(azanedyil))dibenzoic acid(Sq_tpdc),which is identical in directionality and length to tpdc but which contains organocatalytic squaramide centers.Squaramides were chosen because their immobilization into a framework enhances its reactivity and stability while avoiding any self-quenching phenomena.Therefore,the four MOFs share the same organocatalytic squaramide moiety,but confine it within distinct pore environments.We then evaluated these MOFs as heterogeneous H-bonding catalysts in organic transformations:a Friedel-Crafts alkylation and an epoxide ring-opening.Some of them exhibited good performance in both reactions but all showed distinct catalytic profiles that reflect their structural differences.展开更多
The presence of process-induced strains induced by various manufacturing and operational factors is one of the characteristics of polymer composite materials(PCM).Conventional methods of registration and evaluation of...The presence of process-induced strains induced by various manufacturing and operational factors is one of the characteristics of polymer composite materials(PCM).Conventional methods of registration and evaluation of process-induced strains can be laborious,time-consuming and demanding in terms of technical applications.The employment of embedded fibre-optic strain sensors(FOSS)offers a real prospect of measuring residual strains.This paper demonstrates the potential for using embedded FOSS for recording technological strains in a PCM plate.The PCM plate is manufactured from prepreg,using the direct compression-moulding method.In this method,the prepared reinforcing package is placed inside a mould,heated,and then exposed to compaction pressure.The examined technology can be used for positioning FOSS between the layers of the composite material.Fibre-optic sensors,interacting with the material of the examined object,make it possible to register the evolution of the strain process during all stages of polymer-composite formation.FOSS data were recorded with interrogator ASTRO X 327.The obtained data were processed using specially developed algorithms.展开更多
The synthesis and characterization of platinum(II)and palladium(II)complexes bearing two(dimers Pt(L_(pc))_(2)Cl_(2)and Pd(L_(pc))_(2)Cl_(2)),one(monomers Pt(L_(pc))(L_(ref))Cl_(2)and Pd(L_(pc))(L_(ref))-Cl_(2)),or no...The synthesis and characterization of platinum(II)and palladium(II)complexes bearing two(dimers Pt(L_(pc))_(2)Cl_(2)and Pd(L_(pc))_(2)Cl_(2)),one(monomers Pt(L_(pc))(L_(ref))Cl_(2)and Pd(L_(pc))(L_(ref))-Cl_(2)),or no(reference compounds Pt(L_(ref))_(2)Cl_(2)and Pd(L_(ref))_(2)Cl_(2))pentacene-based pyridyl ligands are presented.Photophysical properties of the dimers are probed by means of steady-state and time-resolved transient absorption measurements in compar-ison to the monomer and model compounds.Our results document that despite enhanced spin−orbit coupling from the presence of heavy atoms,intramolecular singlet fission(iSF)is not challenged by intersystem crossing.iSF thus yields correlated triplet pairs and even uncorrelated triplet excited states upon decoherence.Importantly,significant separation of the two pentacenyl groups facilitates decoupling of the two chromophores.Furthermore,the mechanism of iSF is altered depending on the respective metal center,that is,Pt(II)versus Pd(II).The dimer based on Pt(II),Pt(L_(pc))2Cl_(2),exhibits a direct pathway for the iSF and forms a correlated triplet pair with singlet−quintet spin-mixing within 10 ns in variable solvents.On the other hand,the dimer based on Pd(II),Pd(L_(pc))_(2)Cl_(2),leads to charge transfer mixing during the population of the correlated triplet pair that is dependent on solvent polarity.Moreover,Pd(L_(pc))_(2)Cl_(2)gives rise to a stable equilibrium between singlet and quintet correlated triplet pairs with lifetimes of up to 170 ns.Inherent differences in the size and polarizability,when contrasting platinum(II)with palladium(II),are the most likely rationale for the underlying trends.展开更多
基金supported by Russian Science Foundation Grant RSF-22-19-20106。
文摘The article presents an experimental study on the flow of an eutectic gallium alloy in a cylindrical cell,which is placed in an alternating magnetic field.The magnetic field is generated by a coil connected to an alternating current source.The coil is located at a fixed height in such a way that its plane is perpendicular to the gravity vector,which in turn is parallel to the axis of the cylinder.The position of the cylinder can vary in height with respect to the coil.The forced flow of the considered electrically conductive liquid is generated due to the action of the localized electromagnetic force.It is assumed that under the action of the alternating magnetic field,the liquid is heated uniformly,and the resulting heat is quickly absorbed by the forced flow,so that liquid free convection can be neglected.The experiment is carried out using an ultrasonic Doppler anemometer.One transducer is installed in the axially located cylinder sluice and the other transducer is placed in the near-wall region.According to the results,a velocity profile,corresponding to a two-tori flow pattern can be hardly obtained in the low frequency range of the power supply.However,this is possible in the high frequency range.The average velocity profiles depend essentially on the location of the coil relative to the cell.The spectral analysis of velocity signals shows that the amplitude of the velocity pulsations is comparable to the average value of the flow velocity.Such experimental results and their verification through comparison with numerical calculations are intended to support the development of new methods for reducing the intensity of vortex flows during the electromagnetic separation of impurities through an electromagnetic induction mechanism(able to produce an electromotive force that displaces particles).
文摘CONSPECTUS:Efficient photovoltaics(PV)require capturing and converting solar energy across a broad range of energy.Losses due to thermalization and sub-bandgap photons place,however,significant boundaries on the performance of solar cells.For conventional singlejunction cells,the theoretical maximum power conversion efficiency is capped at 33%,a constraint known as the detailed balance limit.Realizing the full potential of PVs requires developing novel strategies to overcome this fundamental obstacle.This Account describes the photon-management capabilities of acenes and addresses these fundamental losses enroute toward enhancing PV performances.For high-energy photons that exceed the semiconductor’s bandgap energy,singlet fission(SF)is a down-conversion pathway to mitigate thermalization losses.SF is a process in organic materials,in which a singlet excited state is split into two independent triplet excited states,effectively doubling the number of charge carriers.Pentacenes stand out among acenes due to their exergonic nature of SF.Numerous molecular pentacene dimers have been synthesized to elucidate the relationship between structure and enhancing SF efficiency.A broader light-harvesting range of SF materials is realized by covalently attaching complementary absorbing energy donors to set up energy donor−acceptor conjugates.Förster resonance energy transfer(FRET)is operative in these energy donor-acceptor conjugates,effectively extending the absorption of SF materials,as the energy donor efficiently transfers its absorbed excitation energy to the energy acceptor.Our studies on various binding motifs show that FRET efficiency depends not only on parameters like the energy donor−acceptor distance and spectral overlap but also on subtle factors such as the alignment of transition dipoles,which significantly affect the energy transfer dynamics and efficiency.Turning to low-energy photons,triplet−triplet annihilation up-conversion(TTA-UC)provides a means of light up-conversion and,thereby,the reduction of sub-bandgap losses.In TTA-UC,a singlet excited state that is potent enough to generate charge carriers is formed by combining two triplet excitons.It is effectively the reverse process of SF.The higher triplet energy of tetracene and an endergonic SF renders them highly effective for TTA-UC.We focus on various tetracene-based systems that maximize TTA-UC efficiency.Besides TTA-UC,two-photon absorption(TPA)is yet another mechanism to leverage below-bandgap photons.It is a nonlinear optical(NLO)process,and acenes reveal NLO properties that are essential for extending light absorption into the near-infrared and still powering SF.We demonstrate in our proof-of-concept studies how TPA further broadens the application potential of acenes for PV systems.The strategies outlined in this Account illustrate that acenes are valuable for addressing mechanistic losses in conventional solar cells.In the final section,we examine light storage following SF by means of interfacial electron transfer.Efficient charge-injection powered by SF materials still requires more research before being implemented in large-scale PV designs.Overall,the advances discussed in this Account not only highlight the pivotal role of acenes as model systems to investigate photon down-and up-conversion processes but also paint a promising picture that more efficient solar energy conversion schemes exceeding the detailed-balance limit can be realized by implementing these materials.
基金funding from the European Union’s Horizon Europe research and Innovation Programme under grant agreement No.101098597(Piezo4Spine)supported by grant PID2020-113480RB-I00 funded by MCIN/AEI/10.13039/501100011033/supported by the Spanish State Funding Agency through project PID2022-139776NB-C66.
文摘Millions of patients and their caretakers live and deal with the devastating consequences of spinal cord injury(SCI)worldwide.Despite outstanding advances in the field to both understand and tackle these pathologies,a cure for SCI patients,with their peculiar characteristics,is still a mirage.One of the most promising therapeutic strategies to date for these patients involves the use of epidural electrical stimulation.In this context,electrically active materials such as graphene and its derivates become particularly interesting.Indeed,solid evidence of their capacity to closely interact with neural cells and networks is growing.Encouraged by previous findings in our laboratory on the exploration of 3D porous reduced graphene oxide(rGO)scaffolds in chronic cervical hemisected rats(C6),herein we report their neuro-reparative properties when chronically implanted in complete transected rats(T9-T10),in which no preserved contralateral neural networks can assist in any observed recovery.Electrophysiological recordings from brainstem regions show antidromic activation of a small population of neurons in response to electrical stimulation caudal to the injury.These neurons are located in the Gigantocellular nucleus of reticular formation and vestibular nuclei,both regions directly related to motor functions.Together with histological features at the lesion site,such as more abundant and larger blood vessels and more abundant,longer and more homogeneously distributed axons,our results corroborate that rGO scaffolds create a permissive environment that allows the invasion of functional axonic processes from neurons located in brainstem nuclei with motor function in a rat model of complete thoracic transection.Additionally,behavioral tests evidence that these scaffolds play an important role in whole-body mechanical stabilization(postural control)proved by the absence of scoliosis,a higher trunk stability and a larger cervico-thoraco-lumbar movement range in rGO-implanted rats.
文摘Here,we propose a method to determine the thickness of the most common transition metal dichalcogenides (TMDCs) placed on the surface of transparent stamps,used for the deterministic placement of two-dimensional materials,by analyzing the red,green and blue channels of transmission-mode optical microscopy images of the samples.In particular,the blue channel transmittance shows a large and monotonic thickness dependence,making it a very convenient probe of the flake thickness.The method proves to be robust given the small flake-to-flake variation and the insensitivity to doping changes of MoS2.We also tested the method for MoSe2,WS2 and WSe2.These results provide a reference guide to identify the number of layers of this family of materials on transparent substrates only using optical microscopy.
基金The reported study was funded by Russian Foundation for Basic Research[17-41-590152].
文摘This paper considers the problem of natural vibrations of a deformable structure containing elements made of piezomaterials.The piezoelectric elements are connected through electrodes to an external electric circuit,which consists of resistive,inductive and capacitive elements.Based on the solution of this problem,the parameters of external electric circuits are searched for to allow optimal passive control of the structural vibrations.The solution to the problem is complex natural vibration frequencies,the real part of which corresponds to the circular eigenfrequency of vibrations and the imaginary part corresponds to its damping rate(damping ratio).The analysis of behaviour of the imaginary parts of complex eigenfrequencies in the space of external circuit parameters allows one to damp given modes of structure vibrations.The effectiveness of the proposed approach is demonstrated using a cantilever-clamped plate and a shell structure in the form of a semi-cylinder connected to series resonant RL circuits.
基金the Spanish MINECO(projects RTI2018-095622-B-I00,RTI2018-095038-B-I00)the Catalan AGAUR(project 2017 SGR 238)+1 种基金the ERC under the EU FP7(ER C-Co 615954)European Unions Horizon 2020 research and innovation program under grant agreement No.685727,and European Structural Funds(S2018/NMT-4367).It was alsofunded by the CERCA Program/Generalitat de Catalunya.ICN2 is supported by the Severo Ochoa program from the Spanish MINECO(G rant No.SEV-2017-0706).
文摘A well-established strategy to synthesize heterogeneous,metal-organic framework(MOF)catalysts that exhibit nanoconfinement effects,and specific pores with highly-localized catalytic sites,is to use organic linkers containing organocatalytic centers.Here,we report that by combining this linker approach with reticular chemistry,and exploiting three-dimensioanl(3D)MOF-structural data from the Cambridge Structural Database,we have designed four heterogeneous MOF-based catalysts for standard organic transformations.These programmable MOFs are isoreticular versions of pcu IRMOF-16,feu UiO-68 and pillared-pcu SNU-8X,the three most common topologies of MOFs built from the organic linker p.p'-terphenyldicarboxylic acid(tpdc).To synthesize the four squaramide-based MOFs,we designed and synthesized a linker,4,4’-((3,4-dioxocyclobut-1-ene-1,2-diyl)bis(azanedyil))dibenzoic acid(Sq_tpdc),which is identical in directionality and length to tpdc but which contains organocatalytic squaramide centers.Squaramides were chosen because their immobilization into a framework enhances its reactivity and stability while avoiding any self-quenching phenomena.Therefore,the four MOFs share the same organocatalytic squaramide moiety,but confine it within distinct pore environments.We then evaluated these MOFs as heterogeneous H-bonding catalysts in organic transformations:a Friedel-Crafts alkylation and an epoxide ring-opening.Some of them exhibited good performance in both reactions but all showed distinct catalytic profiles that reflect their structural differences.
基金The results of sections 2 and 3 were obtained within the RSF grant[project No.14-29-00172-Π]The result s of sections 4 and 5 were obtained within the RFBR[project No.17-41-590684 r-ural-a].
文摘The presence of process-induced strains induced by various manufacturing and operational factors is one of the characteristics of polymer composite materials(PCM).Conventional methods of registration and evaluation of process-induced strains can be laborious,time-consuming and demanding in terms of technical applications.The employment of embedded fibre-optic strain sensors(FOSS)offers a real prospect of measuring residual strains.This paper demonstrates the potential for using embedded FOSS for recording technological strains in a PCM plate.The PCM plate is manufactured from prepreg,using the direct compression-moulding method.In this method,the prepared reinforcing package is placed inside a mould,heated,and then exposed to compaction pressure.The examined technology can be used for positioning FOSS between the layers of the composite material.Fibre-optic sensors,interacting with the material of the examined object,make it possible to register the evolution of the strain process during all stages of polymer-composite formation.FOSS data were recorded with interrogator ASTRO X 327.The obtained data were processed using specially developed algorithms.
文摘The synthesis and characterization of platinum(II)and palladium(II)complexes bearing two(dimers Pt(L_(pc))_(2)Cl_(2)and Pd(L_(pc))_(2)Cl_(2)),one(monomers Pt(L_(pc))(L_(ref))Cl_(2)and Pd(L_(pc))(L_(ref))-Cl_(2)),or no(reference compounds Pt(L_(ref))_(2)Cl_(2)and Pd(L_(ref))_(2)Cl_(2))pentacene-based pyridyl ligands are presented.Photophysical properties of the dimers are probed by means of steady-state and time-resolved transient absorption measurements in compar-ison to the monomer and model compounds.Our results document that despite enhanced spin−orbit coupling from the presence of heavy atoms,intramolecular singlet fission(iSF)is not challenged by intersystem crossing.iSF thus yields correlated triplet pairs and even uncorrelated triplet excited states upon decoherence.Importantly,significant separation of the two pentacenyl groups facilitates decoupling of the two chromophores.Furthermore,the mechanism of iSF is altered depending on the respective metal center,that is,Pt(II)versus Pd(II).The dimer based on Pt(II),Pt(L_(pc))2Cl_(2),exhibits a direct pathway for the iSF and forms a correlated triplet pair with singlet−quintet spin-mixing within 10 ns in variable solvents.On the other hand,the dimer based on Pd(II),Pd(L_(pc))_(2)Cl_(2),leads to charge transfer mixing during the population of the correlated triplet pair that is dependent on solvent polarity.Moreover,Pd(L_(pc))_(2)Cl_(2)gives rise to a stable equilibrium between singlet and quintet correlated triplet pairs with lifetimes of up to 170 ns.Inherent differences in the size and polarizability,when contrasting platinum(II)with palladium(II),are the most likely rationale for the underlying trends.
