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A “Gaussian” for diffusion on the sphere 球面上扩散的“高斯”
EPL (Europhysics Letters) Pub Date : 2012-05-08 DOI: 10.1209/0295-5075/98/30003
Abhijit Ghosh, J. Samuel, S. Sinha
{"title":"A “Gaussian” for diffusion on the sphere","authors":"Abhijit Ghosh, J. Samuel, S. Sinha","doi":"10.1209/0295-5075/98/30003","DOIUrl":"https://doi.org/10.1209/0295-5075/98/30003","url":null,"abstract":"We present an analytical closed form expression, which gives a good approximate propagator for diffusion on the sphere. Our formula is the spherical counterpart of the Gaussian propagator for diffusion on the plane. While the analytical formula is derived using saddle point methods for short times, it works well even for intermediate times. Our formula goes beyond conventional “short time heat kernel expansions\" in that it is nonperturbative in the spatial coordinate, a feature that is ideal for studying large deviations. Our work suggests a new and efficient algorithm for numerical integration of the diffusion equation on a sphere. We perform Monte Carlo simulations to compare the numerical efficiency of the new algorithm with the older Gaussian one.","PeriodicalId":171520,"journal":{"name":"EPL (Europhysics Letters)","volume":"35 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2012-05-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116421186","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 30
Casimir effect of an ideal Bose gas trapped in a generic power-law potential 困在一般幂律势中的理想玻色气体的卡西米尔效应
EPL (Europhysics Letters) Pub Date : 2012-05-01 DOI: 10.1209/0295-5075/98/40010
T. Lin, G. Su, Q. Wang, Jincan Chen
{"title":"Casimir effect of an ideal Bose gas trapped in a generic power-law potential","authors":"T. Lin, G. Su, Q. Wang, Jincan Chen","doi":"10.1209/0295-5075/98/40010","DOIUrl":"https://doi.org/10.1209/0295-5075/98/40010","url":null,"abstract":"The Casimir effect of an ideal Bose gas trapped in a generic power-law potential and confined between two slabs with Dirichlet, Neumann, and periodic boundary conditions is investigated systematically, based on the grand potential of the ideal Bose gas, the Casimir potential and force are calculated. The scaling function is obtained and discussed. The special cases of free and harmonic potentials are also discussed. It is found that when T⩽Tc (where Tc is the critical temperature of Bose-Einstein condensation), the Casimir force is a power-law decay function; when T>Tc, the Casimir force is an exponential decay function; and when T≫Tc, the Casimir force vanishes.","PeriodicalId":171520,"journal":{"name":"EPL (Europhysics Letters)","volume":"67 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2012-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125737678","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 5
Experimental evidence of existence of the axial magnetic field in a plasma focus 等离子体焦点中轴向磁场存在的实验证据
EPL (Europhysics Letters) Pub Date : 2012-05-01 DOI: 10.1209/0295-5075/98/45001
V. Krauz, K. Mitrofanov, M. Scholz, M. Paduch, P. Kubes, L. Karpiński, E. Zielińska
{"title":"Experimental evidence of existence of the axial magnetic field in a plasma focus","authors":"V. Krauz, K. Mitrofanov, M. Scholz, M. Paduch, P. Kubes, L. Karpiński, E. Zielińska","doi":"10.1209/0295-5075/98/45001","DOIUrl":"https://doi.org/10.1209/0295-5075/98/45001","url":null,"abstract":"The magnetic field distribution substantially affects mechanisms for the generation of radiation in Z-pinches. Investigation of the axial component of the magnetic field is one of the important problems in plasma focus studies. The measurements of the Bz-component of the magnetic field on the PF-1000 facility were done with the multichannel absolutely calibrated probe both at the stage of plasma-current sheath radial compression and in the dense-pinch stage. In the compression stage, the axial component of the magnetic field reaches several kG that comprises ∼10% of the azimuthal component. The presence of the Bz field is a powerful argument in favor of the existence of closed magnetic configurations, which play an important role in the generation of neutrons.","PeriodicalId":171520,"journal":{"name":"EPL (Europhysics Letters)","volume":"64 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2012-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121921898","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 39
Concentration of point defects in wurtzite AlN: A hybrid functional study 纤锌矿AlN中点缺陷的集中:一种杂化功能研究
EPL (Europhysics Letters) Pub Date : 2012-05-01 DOI: 10.1209/0295-5075/98/36003
L. Silvestri, K. Dunn, S. Prawer, F. Ladouceur
{"title":"Concentration of point defects in wurtzite AlN: A hybrid functional study","authors":"L. Silvestri, K. Dunn, S. Prawer, F. Ladouceur","doi":"10.1209/0295-5075/98/36003","DOIUrl":"https://doi.org/10.1209/0295-5075/98/36003","url":null,"abstract":"Formation energies and concentrations of the most relevant point defects in n-type wurtzite AlN are obtained by first-principle calculations employing a hybrid functional. We show that the incorporation of Si is favoured over O under N-rich growth conditions, but not under Al-rich conditions. The triply negatively charged Al vacancy is found to be the defect with the lowest formation energy in n-type AlN and it is therefore expected to be the main compensating acceptor. Under typical physical vapor-phase transport growth conditions, we predict Si concentrations of up to 1020 cm− 3 and net donor concentrations of about 1018 cm− 3, in good agreement with available experimental data.","PeriodicalId":171520,"journal":{"name":"EPL (Europhysics Letters)","volume":"18 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2012-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132225062","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 14
Ground state of classical bilayer Wigner crystals 经典双层维格纳晶体的基态
EPL (Europhysics Letters) Pub Date : 2012-05-01 DOI: 10.1209/0295-5075/98/36004
L. Šamaj, E. Trizac
{"title":"Ground state of classical bilayer Wigner crystals","authors":"L. Šamaj, E. Trizac","doi":"10.1209/0295-5075/98/36004","DOIUrl":"https://doi.org/10.1209/0295-5075/98/36004","url":null,"abstract":"We study the ground-state structure of electronic-like bilayers, where different phases compete upon changing the inter-layer separation or particle density. New series representations with exceptional convergence properties are derived for the exact Coulombic energies under scrutiny. The complete phase transition scenario —including critical phenomena— can subsequently be worked out in detail, thereby unifying a rather scattered or contradictory body of literature, hitherto plagued by the inaccuracies inherent to long-range interaction potentials.","PeriodicalId":171520,"journal":{"name":"EPL (Europhysics Letters)","volume":"131 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2012-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131013224","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 15
A high intensity 6He beam for the β-beam neutrino oscillation facility 用于β束中微子振荡装置的高强度6He束
EPL (Europhysics Letters) Pub Date : 2012-05-01 DOI: 10.1209/0295-5075/98/32001
T. Stora, E. Noah, R. Hodak, T. Hirsh, M. Hass, Vivek Kumar, Kuljeet Singh, S. Vaintraub, P. Delahaye, H. Franberg-Delahaye, M. Saint-Laurent, G. Lhersonneau
{"title":"A high intensity 6He beam for the β-beam neutrino oscillation facility","authors":"T. Stora, E. Noah, R. Hodak, T. Hirsh, M. Hass, Vivek Kumar, Kuljeet Singh, S. Vaintraub, P. Delahaye, H. Franberg-Delahaye, M. Saint-Laurent, G. Lhersonneau","doi":"10.1209/0295-5075/98/32001","DOIUrl":"https://doi.org/10.1209/0295-5075/98/32001","url":null,"abstract":"This work presents the production and extraction of the short-lived radionuclide 6He in yet unmatched yields from the ISOLDE facility at CERN. It is the first report of 6He production using spallation neutrons via the 9Be(n, α)6He reaction. These neutrons are produced from the 1.4 GeV proton beam of the Proton Synchrotron Booster (PSB) striking a tungsten converter, and are impinging on a porous BeO material. The central position of 6He in future experiments is due to its role as a necessary radioactive nucleus to realize the β-beam at CERN, a next-generation facility to study neutrino oscillation parameters, and hence neutrino masses. In the β-beam scenario, an intense beam of radioactive 6He nuclei will be produced, accelerated to multi-GeV energies and stored in a dedicated storage ring. The resulting virtually mono-directional anti-neutrino beam from the decay of the stored 6He nuclei will be directed towards a remote underground neutrino detector. A similar beam of, e.g., 18Ne will provide neutrinos, an ideal concept to test CP violation in the neutrino sector. The results of the present experiment demonstrate for the first time that the necessary conditions for the realization of the proposed β-beam scheme with anti-neutrinos can be fulfilled.","PeriodicalId":171520,"journal":{"name":"EPL (Europhysics Letters)","volume":"136 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2012-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115885794","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 21
Quantum vacuum influence on pulsars spindown evolution 量子真空对脉冲星自旋演化的影响
EPL (Europhysics Letters) Pub Date : 2012-05-01 DOI: 10.1209/0295-5075/98/49001
A. Dupays, C. Rizzo, Giovanni Fabrizio Bignami
{"title":"Quantum vacuum influence on pulsars spindown evolution","authors":"A. Dupays, C. Rizzo, Giovanni Fabrizio Bignami","doi":"10.1209/0295-5075/98/49001","DOIUrl":"https://doi.org/10.1209/0295-5075/98/49001","url":null,"abstract":"In this letter, we show that Quantum Vacuum Friction (QVF) resulting from the interaction between the magnetic dipole moment of a pulsar and its induced quantum vacuum magnetic dipole moment should play an important role in how a neutron star's spin period evolves. Taking into account this effect we show that magnetars could be understood as a natural evolution of standard pulsars. In particular, for the Crab pulsar, of which the true age is known, we present the first completely coherent time evolution for its period and braking index. For this pulsar and for the B1509-58 pulsar we also give the predicted values of the current first derivative of the braking index that we compare with existing experimental data. Our prediction provides a very important test to confirm or invalidate QVF.","PeriodicalId":171520,"journal":{"name":"EPL (Europhysics Letters)","volume":"116 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2012-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"117217960","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 11
A note on the thermodynamics of self-gravitating systems and its related astrophysics 关于自引力系统的热力学及其相关天体物理学的注解
EPL (Europhysics Letters) Pub Date : 2012-05-01 DOI: 10.1209/0295-5075/98/30011
Dong-Biao Kang
{"title":"A note on the thermodynamics of self-gravitating systems and its related astrophysics","authors":"Dong-Biao Kang","doi":"10.1209/0295-5075/98/30011","DOIUrl":"https://doi.org/10.1209/0295-5075/98/30011","url":null,"abstract":"Our previous works have shown the statistical mechanics of self-gravitating system. In this paper, we will first further analyse the physics behind it and propose that our statistical mechanics can be based on local ergodicity and Boltzmann entropy. With the method of statistical mechanics, we will show our definition of temperature and then the capacity of self-gravitating systems. Then we will preliminarily show the thermal stability of the thermodynamical equilibrium state in our theory. Our results also provide new explanations for observations and numerical simulations of dissipationless collapse, including that the gravothermal catastrophe may be only a special case of our results, and the non-universal density distribution in the simulations of dissipationless collapse may be not caused by a different initial collapse factor.","PeriodicalId":171520,"journal":{"name":"EPL (Europhysics Letters)","volume":"92 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2012-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127337580","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 4
Anisotropy of homogenized phononic crystals with anisotropic material 具有各向异性材料的均匀声子晶体的各向异性
EPL (Europhysics Letters) Pub Date : 2012-05-01 DOI: 10.1209/0295-5075/98/36001
Jun Liu, Yihui Wu, Feng Li, Ping Zhang, Yongshun Liu, Junfeng Wu
{"title":"Anisotropy of homogenized phononic crystals with anisotropic material","authors":"Jun Liu, Yihui Wu, Feng Li, Ping Zhang, Yongshun Liu, Junfeng Wu","doi":"10.1209/0295-5075/98/36001","DOIUrl":"https://doi.org/10.1209/0295-5075/98/36001","url":null,"abstract":"The anisotropy of elastic waves propagating in two-dimension phononic crystals with cubic crystal material was theoretically investigated in the long wavelength limit. The anisotropy can be tuned efficiently by either rotating the crystalline orientation of the material or changing the filling fraction. It can even disappear at a given orientation and filling fraction. The pure vibration mode direction and the pure propagation mode direction can be efficiently tuned to a desired direction deviating from the symmetric plane of the phononic crystal lattice. These results will be useful in manipulating the anisotropy of a homogenized composite and dealing with a PC with anisotropic material.","PeriodicalId":171520,"journal":{"name":"EPL (Europhysics Letters)","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2012-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129942601","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 8
Counterfactual attack on counterfactual quantum key distribution 反事实量子密钥分发的反事实攻击
EPL (Europhysics Letters) Pub Date : 2012-05-01 DOI: 10.1209/0295-5075/98/30012
Sheng Zhang, Jian Wnang, Chaojing Tang
{"title":"Counterfactual attack on counterfactual quantum key distribution","authors":"Sheng Zhang, Jian Wnang, Chaojing Tang","doi":"10.1209/0295-5075/98/30012","DOIUrl":"https://doi.org/10.1209/0295-5075/98/30012","url":null,"abstract":"It is interesting that counterfactual quantum cryptography protocols allow two remotely separated parties to share a secret key without transmitting any signal particles. Generally, these protocols, expected to provide security advantages, base their security on a translated no-cloning theorem. Therefore, they potentially exhibit unconditional security in theory. In this letter, we propose a new Trojan horse attack, by which an eavesdropper Eve can gain full information about the key without being noticed, to real implementations of a counterfactual quantum cryptography system. Most importantly, the presented attack is available even if the system has negligible imperfections. Therefore, it shows that the present realization of counterfactual quantum key distribution is vulnerable.","PeriodicalId":171520,"journal":{"name":"EPL (Europhysics Letters)","volume":"19 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2012-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127848663","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 14
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