Department of Physics

Department of Physics
Xi'an Jiaotong-Liverpool University
111 Ren'ai Road Suzhou Dushu Lake Science and Education Innovation District , Suzhou Industrial Park
Suzhou,Jiangsu Province,P. R. China,215123

1. Deformations of the standard model: SUq(3) flavor symmetry

Author:Gresnigt, NG


Abstract:The quantum group SUq(3) = Uq(su(3)) is taken as a baryon flavor symmetry and exceptionally accurate octet and decuplet baryons mass relations are obtained by accounting for the electromagnetic contribution to baryon masses (to zeroth order). The resulting charge specific q-deformed octet and decuplet baryon mass sum formulas are accurate to 0.02%% and 0.08%% respectively; a factor of 20 reduction in error compared to the standard Gell-Mann-Okubo mass formulas. An explicit formula for the Cabibbo angle, taken to be pi/14, in terms of the deformation parameter q and spin parity J(P) of the baryons is obtained.
2. The formation of binary star clusters in the Milky Way and Large Magellanic Cloud

Author:Darma, R;Arifyanto, MI;Kouwenhoven, MBN


Abstract:Recent observations of young embedded clumpy clusters and statistical identifications of binary star clusters have provided new insights into the formation process and subsequent dynamical evolution of star clusters. The early dynamical evolution of clumpy stellar structures provides the conditions for the origin of binary star clusters. Here, we carry out N-body simulations in order to investigate the formation of binary star clusters in the MilkyWay and in the Large Magellanic Cloud (LMC). We find that binary star clusters can form from stellar aggregates with a variety of initial conditions. For a given initial virial ratio, a higher degree of initial substructure results in a higher fraction of binary star clusters. The number of binary star clusters decreases over time due to merging or dissolution of the binary system. Typically, similar to 45 per cent of the aggregates evolve into binary/multiple clusters within t = 20 Myr in the Milky Way environment, while merely similar to 30 per cent survives beyond t = 50 Myr, with separations <= 50 pc. On the other hand, in the LMC, similar to 90 per cent of the binary/multiple clusters survive beyond t = 20 Myr and the fraction decreases to similar to 80 per cent at t = 50 Myr, with separations less than or similar to 35 pc. Multiple clusters are also rapidly formed for highly substructured and expanding clusters. The additional components tend to detach and the remaining binary star cluster merges. The merging process can produce fast rotating star clusters with mostly flat rotation curves that speed up in the outskirts.
3. Polygonal rotopulsators of the curved n-body problem

Author:Tibboel, P


Abstract:We revisit polygonal positive elliptic rotopulsator solutions and polygonal negative elliptic rotopulsator solutions of the n-body problem in H-3 and S-3 and prove the existence of these solutions and prove that the masses of these rotopulsators have to be equal if the rotopulsators are of nonconstant size and show that the number of negative elliptic relative equilibria of this type is finite, as is the number of positive elliptic relative equilibria if an upper bound on the size of the relative equilibrium is imposed. Additionally, we prove that a class of negative hyperbolic rotopulsators is in fact a subclass of the class of polygonal negative elliptic rotopulsators. Published by AIP Publishing.
4. Strong quantum confinement effect and reduced Frohlich exciton-phonon coupling in ZnO quantum dots embedded inside a SiO2 matrix

Author:Ning, JQ;Zheng, CC;Zhang, XH;Xu, SJ


Abstract:ZnO quantum dots (QDs) embedded in an amorphous SiO2 matrix were examined in depth by using variable-temperature photoluminescence (PL) and optical reflectance spectroscopies. Compared with ZnO bulk crystals, ZnO quantum dots with an average size of 4 nm exhibit a strong quantum confinement effect, evidenced by a large blue shift in both PL and reflectance peaks of excitons. More interestingly, a remarkably reduced long-range Frohlich interaction was revealed in ZnO QDs. These fascinating effects may make ZnO QDs a very appealing system in the fields of optoelectronics and others.
5. The Long-term Evolution of Main-sequence Binaries in DRAGON Simulations

Author:Shu, Q;Pang, XY;Dotti, FF;Kouwenhoven, MBN;Sedda, MA;Spurzem, R


Abstract:We present a comprehensive investigation of main-sequence binaries in the DRAGON simulations, which are the first one-million-particle direct N-body simulations of globular clusters. We analyze the orbital parameters of the binary samples in two of the DRAGON simulations, D1-R7-IMF93 and D2-R7-IMF01, focusing on their secular evolution and correlations up to 12 Gyr. These two models have different initial stellar mass functions: Kroupa 1993 (D1-R7-IMF93) and Kroupa 2001 (D2-R7-IMF01); and different initial mass-ratio distributions: random paring (D1-R7-IMF93) and a power law (D1-R7-IMF93). In general, the mass ratio of a population of binaries increases over time due to stellar evolution, which is less significant in D2-R7-IMF01. In D1-R7-IMF93, primordial binaries with a mass ratio q 0.2 are most common, and the frequency linearly declines with increasing q at all times. Dynamical binaries of both models have higher eccentricities and larger semimajor axes than primordial binaries. They are preferentially located in the inner part of the star cluster. Secular evolution of binary orbital parameters does not depend on the initial mass-ratio distribution, but is sensitive to the initial binary distribution of the system. At t = 12 Gyr, the binary fraction decreases radially outwards, and mass segregation is present. A color difference of 0.1 mag in F330W - F814W and 0.2 mag in NUV - y between the core and the outskirts of both clusters is seen, which is a reflection of the binary radial distribution and the mass segregation in the cluster. The complete set of data for primordial and dynamical binary systems at all snapshot intervals is made publicly available.
6. A Catalog of Newly Identified Star Clusters in Gaia DR2

Author:Liu, L;Pang, XY


Abstract:We present the Star cluster Hunting Pipeline (SHiP) that can identify star clusters in Gaia second data release (DR2) data and establish a star cluster catalog for the Galactic disk. A friend-of-friend-based cluster finder method is used to identify star clusters using five-dimensional stellar parameters, l, b, omega, mu(alpha) cos delta, and mu(delta). Our new catalog contains 2443 star cluster candidates identified from disk stars located within vertical bar b vertical bar = 25. and with G < 18 mag. An automatic isochrone fitting scheme is applied to all cluster candidates. With a combination of parameters obtained from isochrone fitting, we classify cluster candidates into three classes (Class 1, 2, and 3). Class 1 clusters are the most probable star cluster candidates with the most stringent criteria. Most of these clusters are nearby (within 4 kpc). Our catalog is crossmatched with three Galactic star cluster catalogs, Kharchenko et al., Gaudin et al., and Bica et al. The proper motion and parallax of matched star clusters are in good agreement with these earlier catalogs. We discover 76 new star cluster candidates that are not listed in these three catalogs. The majority of these are clusters older than log(age/yr) = 8.0 and are located in the inner disk with vertical bar b vertical bar < 5 degrees. The recent discovery of new star clusters suggests that current Galactic star cluster catalogs are still incomplete. Among the Class 1 cluster candidates, we find 56 candidates for star cluster groups. The pipeline, the catalog, and the member list containing all candidates star clusters and star cluster groups have been made publicly available.
7. Electrospinning preparation of Sn4+-doped BiFeO3 nanofibers as efficient visible-light-driven photocatalyst for O-2 evolution

Author:Ren, JB;Zhao, D;Liu, HH;Zhong, YJ;Ning, JQ;Zhang, ZY;Zheng, CC;Hu, Y


Abstract:Metal ion doping has been regarded as an effective strategy to improve photocatalytic activity of pristine photocatalysts for rapid charge transfer and separation effects achieved by doping induced defect states. We herein report the fabrication of uniform one-dimensional (1D) Sn4+-doped BiFeO3 (Sn-BFO) nano-fibers (NFs) by a facile electrospinning technique with subsequent annealing treatment. Benefiting from metal ion doping and the unique 1D structure, the as-prepared Sn-BFO NF catalyst exhibits significantly enhanced photocatalytic performance on O-2 evolution as well as improved photostability under visiblelight illumination. Revealed by experimental investigation as well as density functional theory (DFT) calculation, the doped Sn atoms were incorporated into the BFO lattice and the band structure of BFO was effectively modified and the defect-related energy levels were produced, which leads to the boosted light absorption and improved charge transfer and separation efficiency. Additionally, an optimal Sn4+ doping percentage of 1.0%% was discovered to achieve an average O-2 evolution rate of 516.4 mu mol h(-1) g(-1), nearly two times as much as the non-doped BFO samples. (C) 2018 Elsevier B.V. All rights reserved.
8. Putting student partnership and collaboration centre-stage in a research-led context: A case study of the Summer Undergraduate Research Fellowship programme at Xi’an Jiaotong-Liverpool University

Author:Huijser, H., Wilson, J., Wu, Y., Qiu, S., Wang, K., Li, S., Chen, W., & Kouwenhoven, M.

Source:International Journal for Students as Partners,2019,Vol.3

Abstract:In this case study, we evaluated the Summer Undergraduate Research Fellowship (SURF) initiative at Xi’an Jiaotong-Liverpool University (XJTLU), an extracurricular programme that focuses on academic staff-student partnerships and collaborations. While not directly integrated into university degree programmes, SURF provides students with the opportunity to develop practical research skills related to knowledge they have acquired in class. Participating students receive an authentic research experience, which involves collaboration on research projects with academic staff. All students are required to present results of their projects at a public poster presentation event organised by the university. This case study is a partnership between Academic Enhancement Centre (AEC) staff, who organize and run SURF, SURF students, and a lecturer (M.B.N. Kouwenhoven), and it presents a reflection on their experiences of the SURF programme, and in particular on the notions of partnership and collaboration and the potential tension between those two concepts.

Author:Li, Y;Kouwenhoven, MBN;Stamatellos, D;Goodwin, SP


Abstract:The origin of very low-mass hydrogen-burning stars, brown dwarfs (BDs), and planetary-mass objects (PMOs) at the low-mass end of the initial mass function is not yet fully understood. Gravitational fragmentation of circumstellar disks provides a possible mechanism for the formation of such low-mass objects. The kinematic and binary properties of very low-mass objects formed through disk fragmentation at early times (<10 Myr) were discussed in our previous paper. In this paper we extend the analysis by following the long-term evolution of disk-fragmented systems up to an age of 10 Gyr, covering the ages of the stellar and substellar populations in the Galactic field. We find that the systems continue to decay, although the rates at which companions escape or collide with each other are substantially lower than during the first 10 Myr, and that dynamical evolution is limited beyond 1 Gyr. By t = 10 Gyr, about one third of the host stars are single, and more than half have only one companion left. Most of the other systems have two companions left that orbit their host star in widely separated orbits. A small fraction of companions have formed binaries that orbit the host star in a hierarchical triple configuration. The majority of such double-companion systems have internal orbits that are retrograde with respect to their orbits around their host stars. Our simulations allow a comparison between the predicted outcomes of disk fragmentation with the observed low-mass hydrogen-burning stars, BDs, and PMOs in the solar neighborhood. Imaging and radial velocity surveys for faint binary companions among nearby stars are necessary for verification or rejection of the formation mechanism proposed in this paper.
10. Effects of Fe doping on the strain and optical properties of GaN epilayers grown on sapphire substrates

Author:Zheng, CC;Ning, JQ;Wu, ZP;Wang, JF;Zhao, DG;Xu, K;Gao, J;Xu, SJ

Source:RSC ADVANCES,2014,Vol.4

Abstract:The effects of Fe doping on a series of Fe-doped GaN epilayers with different doping concentrations grown on sapphire substrates were investigated in detail by confocal micro-Raman spectroscopy under the back-scattering geometric configuration. Careful investigation of the E-2(high) and A(1)(LO) modes of the Fe- and Si-doped epilayers as well as the intentionally undoped free-standing GaN reveals that the compressive residual strain in the Fe-doped GaN epilayers tends to relax as the Fe concentration increases. This finding is further supported by X-ray diffraction measurements. The relaxation of compressive residual strain is most likely due to compensation by the tensile strain induced by incorporation of iron atoms in the GaN epilayers. The influence of Fe doping on the background electron concentration was also discussed by analyzing the upper branch of the A(1)(LO)-plasmon coupled mode.
11. Clearing Residual Planetesimals by Sweeping Secular Resonances in Transitional Disks: A Lone-planet Scenario for the Wide Gaps in Debris Disks around Vega and Fomalhaut

Author:Zheng, XC;Lin, DNC;Kouwenhoven, MBN;Mao, SD;Zhang, XJ


Abstract:Extended gaps in the debris disks of both Vega and Fomalhaut have been observed. These structures have been attributed to tidal perturbations by multiple super-Jupiter gas giant planets. Within the current observational limits, however, no such massive planets have been detected. Here we propose a less stringent "lone-planet" scenario to account for the observed structure with a single eccentric gas giant and suggest that clearing of these wide gaps is induced by its sweeping secular resonance. With a series of numerical simulations, we show that the gravitational potential of the natal disk induces the planet to precess. At the locations where its precession frequency matches the precession frequency the planet imposes on the residual planetesimals, their eccentricity is excited by its resonant perturbation. Due to the hydrodynamic drag by the residual disk gas, the planetesimals undergo orbital decay as their excited eccentricities are effectively damped. During the depletion of the disk gas, the planet's secular resonance propagates inward and clears a wide gap over an extended region of the disk. Although some residual intermediate-size planetesimals may remain in the gap, their surface density is too low to either produce superEarths or lead to sufficiently frequent disruptive collisions to generate any observable dusty signatures. The main advantage of this lone-planet sweeping-secular-resonance model over the previous multiple gas giant tidal truncation scenario is the relaxed requirement on the number of gas giants. The observationally inferred upper mass limit can also be satisfied provided the hypothetical planet has a significant eccentricity. A significant fraction of solar or more massive stars bear gas giant planets with significant eccentricities. If these planets acquired their present-day kinematic properties prior to the depletion of their natal disks, their sweeping secular resonance would effectively impede the retention of neighboring planets and planetesimals over a wide range of orbital semimajor axes.
12. Unusual formation of tetragonal microstructures from nitrogen-doped carbon nanocapsules with cobalt nanocores as a bi-functional oxygen electrocatalyst

Author:Hu, EL;Ning, JQ;He, B;Li, ZP;Zheng, CC;Zhong, YJ;Zhang, ZY;Hu, Y


Abstract:A facile non-template solid-state reaction method has been developed for the first time preparation of a tetragonal microstructure self-assembled from nitrogen-doped carbon nanocapsules containing metallic cobalt nanoparticles (Co-N-C) by using graphitic carbon nitride (g-C3N4) and Co(CH3COO)(2)center dot 4H(2)O as the only reactants, in which g-C3N4 acts as the effective source of nitrogen and carbon elements in the N-doped carbon nanocapsules and Co(CH3COO)(2)center dot 4H(2)O controls the microscopic structure of the self-assembled product. The as-prepared Co-N-C tetragonal microstructures exhibit enhanced electrocatalytic activities for both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). The synergistic effect of the chemical compositions and the robust microstructure made of the interconnected N-doped carbon nanocapsules accounts for the superior ORR and OER activity and stability to the commercial Pt/C electrocatalyst. The synthetic strategy presented in this work demonstrates a new avenue for developing highly active carbon-based electrocatalysts for electrochemical energy storage and conversion.
13. Influence of curvature strain and Van der Waals force on the inter-layer vibration mode of WS2 nanotubes: A confocal micro-Raman spectroscopic study

Author:Wang, XH;Zheng, CC;Ning, JQ


Abstract:Transition-metal dichalcogenides (TMDs) nanostructures including nanotubes and monolayers have attracted great interests in materials science, chemistry to condensed matter physics. We present an interesting study of the vibration modes in multi-walled tungsten sulfide (WS2) nanotubes prepared via sulfurizing tungsten oxide (WO3) nanowires which are investigated by confocal micro-Raman spectroscopy. The inter-layer vibration mode of WS2 nanotubes, A(1g), is found to be sensitive to the diameter and curvature strain, while the in-plane vibration mode, E-12g,E- is not. A(1g) mode frequency shows a redshift by 2.5 cm(-1) for the multi-layered nanotubes with small outer-diameters, which is an outcome of the competition between the Van der Waals force stiffening and the curvature strain softening. We also show that the Raman peak intensity ratio is significantly different between the 1-2 wall layered nanotubes and monolayer flat sheets.
14. Super transverse diffusion of minority carriers in GaxIn1-xP/GaAs double-junction tandem solar cells

Author:Deng, Z. ; Wang, R.X. ; Ning, J.Q. ; Zheng, C.C. ; Xu, S.J. ; Xing, Z. ; Lu, S.L. ; Dong, J.R. ; Zhang, B.S. ; Yang, H.

Source:Solar Energy,2014,Vol.110

Abstract:In this work, remarkable transverse diffusion of minority carriers in the GaxIn1-xP top subcell of a GaxIn1-xP/GaAs double-junction tandem solar cell is revealed by the electroluminescence (EL) image surveying. As the forward bias is increased, the overall EL intensity rapidly increases, but the topographical distribution of lateral intensity becomes more uneven. By analyzing the relation between the measured EL emission intensity and diffusion parameters of electrically injected minority carriers, the transverse diffusion length of the minority carriers is determined to be ~93μm at the forward bias of 2.75V, which is 30 times larger than that of unbiased GaxIn1-xP single layer. Possible influence of such super diffusion of charge carriers on the conversion efficiency of tandem solar cells is discussed. © 2014 Elsevier Ltd.
15. Cell-type-based model explaining coexpression patterns of genes in the brain

Author:Grange, P;Bohland, JW;Okaty, BW;Sugino, K;Bokil, H;Nelson, SB;Ng, L;Hawrylycz, M;Mitra, PP


Abstract:Spatial patterns of gene expression in the vertebrate brain are not independent, as pairs of genes can exhibit complex patterns of coexpression. Two genes may be similarly expressed in one region, but differentially expressed in other regions. These correlations have been studied quantitatively, particularly for the Allen Atlas of the adult mouse brain, but their biological meaning remains obscure. We propose a simple model of the coexpression patterns in terms of spatial distributions of underlying cell types and establish its plausibility using independently measured cell-typespecific transcriptomes. The model allows us to predict the spatial distribution of cell types in the mouse brain.
16. Photoinduced doping and photoluminescence signature in an exfoliated WS2 monolayer semiconductor

Author:Wang, XH;Ning, JQ;Su, ZC;Zheng, CC;Zhu, BR;Xie, L;Wu, HS;Xu, SJ

Source:RSC ADVANCES,2016,Vol.6

Abstract:Following graphene, atomically thin two-dimensional transition metal dichalcogenides (2D-TMDs) are quickly emerging as a new multidisciplinary frontier across condensed matter physics, materials science and inorganic chemistry. Compared with graphene, the optical and optoelectronic properties of 2D-TMD materials are more attractive largely due to the nature of their direct band gap. In this article, we show an interesting demonstration of the photoinduced doping effect in a mechanically-exfoliated high-quality tungsten disulfide (WS2) monolayer semiconductor. By utilizing a focused laser beam and increasing its intensity, we successfully observed a photoinduced doping effect, indicated by the gradual tuning of dominant light emission from a single narrow emission band peaking at 2.017 eV (Peak 1) to a broad asymmetric emission band (Peak 2) eventually located at around 1.955 eV at room temperature. Moreover, the peak position of Peak 2 shows a distinct red shift dependence on the excitation intensity, predicted by the band gap renormalization theory due to the heavy doping. Justified from their spectral features and excitation intensity dependence, the narrow emission band is ascribed to the fundamental band edge free exciton transition, whereas the broad asymmetric one is ascribed to the localized state ensemble induced by photo doping.
17. Construction of hierarchical FeP/Ni2P hollow nanospindles for efficient oxygen evolution

Author:Feng, YF;Xu, CY;Hu, EL;Xia, BB;Ning, JQ;Zheng, CC;Zhong, YJ;Zhang, ZY;Hu, Y


Abstract:In this work, we demonstrate the design and construction of hierarchical FeP/Ni2P hybrid hollow nanospindles (HNSs) as an active and stable electrocatalyst for the oxygen evolution reaction (OER). Employing solid FeOOH NSs coated with a thin layer of SiO2 as the template and Ni(NO3)(2)center dot 6H(2)O as the reagent, 2D nickel silicate (Ni3Si4O10(OH)(2)center dot 5H(2)O) nanosheets were grown on the surface of the FeOOH spindles through a facile solvothermal method to produce hierarchical FeOOH@Ni3Si4O10(OH)(2)center dot 5H(2)O hybrid NSs. Following a subsequent phosphorization treatment, the as-prepared solid composite NSs were successfully converted into FeP/Ni2P HNSs. The SiO2 nanocoating was found to play a crucial role in this synthesis, and served not only as a reagent for the solvothermal reaction, but also as a nanoreactor for preserving the template morphology after the phosphorization treatment. Benefiting from the unique hollow and hierarchical nanoscaled hybrid structure, the FeP/Ni2P HNS electrocatalyst displays superior electrocatalytic activity for the OER to FexP, Ni2P and the physical mixture of FexP and Ni2P samples, achieving an overpotential of 234 mV at a current density of 10 mA cm(-2) in 1 M KOH and a relatively low Tafel slope of 56 mV dec(-1).
18. Planetary systems in a star cluster I: the Solar system scenario

Author:Dotti, FF;Kouwenhove, MBN;Cai, MX;Spurzem, R


Abstract:Young stars are mostly found in dense stellar environments, and even our own Solar system may have formed in a star cluster. Here, we numerically explore the evolution of planetary systems similar to our own Solar system in star clusters. We investigate the evolution of planetary systems in star clusters. Most stellar encounters are tidal, hyperbolic, and adiabatic. A small fraction of the planetary systems escape from the star cluster within 50 Myr; those with low escape speeds often remain intact during and after the escape process. While most planetary systems inside the star cluster remain intact, a subset is strongly perturbed during the first 50 Myr. Over the course of time, 0.3-5.3 per cent of the planets escape, sometimes up to tens of millions of years after a stellar encounter occurred. Survival rates are highest for Jupiter, while Uranus and Neptune have the highest escape rates. Unless directly affected by a stellar encounter itself, Jupiter frequently serves as a barrier that protects the terrestrial planets from perturbations in the outer planetary system. In low-density environments, Jupiter provides protection from perturbations in the outer planetary system, while in high-density environments, direct perturbations of Jupiter by neighbouring stars is disruptive to habitable-zone planets. The diversity amongst planetary systems that is present in the star clusters at 50 Myr, and amongst the escaping planetary systems, is high, which contributes to explaining the high diversity of observed exoplanet systems in star clusters and in the Galactic field.
19. Towards an emergent model of solitonic particles from non-trivial vacuum structure

Author:Gillard, AB;Gresnigt, NG


Abstract:We motivate and introduce what we refer to as the principles of Lie-stability and Hopf-stability and see what the physical theories must look like. Lie-stability is needed on the classical side and Hopf-stability is needed on the quantum side. We implement these two principles together with Lie deformations consistent with basic constraints on the classical kinematical variables to arrive at the form of a theory that identifies standard model fermions with quantum solitonic trefoil knotted flux tubes which emerge from a flux tube vacuum network. Moreover, twisted unknot fluxtubes form natural dark matter candidates.
20. Run-and-tumble particles on a line with a fertile site

Author:Grange, P;Yao, XQ


Abstract:We propose a model of run-and-tumble particles (RTPs) on a line with a fertile site at the origin. After going through the fertile site, a run-and-tumble particle gives rise to new particles until it flips direction. The process of creation of new particles is modelled by a fertility function (of the distance to the fertile site), multiplied by a fertility rate. If the initial conditions correspond to a single RTP with even probability density, the system is parity-invariant. The equations of motion can be solved in the Laplace domain, in terms of the density of right-movers at the origin. At large time, this density is shown to grow exponentially, at a rate that depends only on the fertility function and fertility rate. Moreover, the total density of RTPs (divided by the density of right-movers at the origin), reaches a stationary state that does not depend on the initial conditions, and presents a local minimum at the fertile site.
Total 119 results found
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