1,042 research outputs found
Evaluating Feynman integrals by the hypergeometry
The hypergeometric function method naturally provides the analytic
expressions of scalar integrals from concerned Feynman diagrams in some
connected regions of independent kinematic variables, also presents the systems
of homogeneous linear partial differential equations satisfied by the
corresponding scalar integrals. Taking examples of the one-loop and
massless functions, as well as the scalar integrals of two-loop vacuum
and sunset diagrams, we verify our expressions coinciding with the well-known
results of literatures. Based on the multiple hypergeometric functions of
independent kinematic variables, the systems of homogeneous linear partial
differential equations satisfied by the mentioned scalar integrals are
established. Using the calculus of variations, one recognizes the system of
linear partial differential equations as stationary conditions of a functional
under some given restrictions, which is the cornerstone to perform the
continuation of the scalar integrals to whole kinematic domains numerically
with the finite element methods. In principle this method can be used to
evaluate the scalar integrals of any Feynman diagrams.Comment: 39 pages, including 2 ps figure
Realization of Zero-Refractive-Index Lens with Ultralow Spherical Aberration
Optical complex materials offer unprecedented opportunity to engineer
fundamental band dispersion which enables novel optoelectronic functionality
and devices. Exploration of photonic Dirac cone at the center of momentum space
has inspired an exceptional characteristic of zero-index, which is similar to
zero effective mass in fermionic Dirac systems. Such all-dielectric zero-index
photonic crystals provide an in-plane mechanism such that the energy of the
propagating waves can be well confined along the chip direction. A
straightforward example is to achieve the anomalous focusing effect without
longitudinal spherical aberration, when the size of zero-index lens is large
enough. Here, we designed and fabricated a prototype of zero-refractive-index
lens by comprising large-area silicon nanopillar array with plane-concave
profile. Near-zero refractive index was quantitatively measured near 1.55 um
through anomalous focusing effect, predictable by effective medium theory. The
zero-index lens was also demonstrated to perform ultralow longitudinal
spherical aberration. Such IC compatible device provides a new route to
integrate all-silicon zero-index materials into optical communication, sensing,
and modulation, and to study fundamental physics on the emergent fields of
topological photonics and valley photonics.Comment: 14 pages, 4 figure
DeepCF: A Unified Framework of Representation Learning and Matching Function Learning in Recommender System
In general, recommendation can be viewed as a matching problem, i.e., match
proper items for proper users. However, due to the huge semantic gap between
users and items, it's almost impossible to directly match users and items in
their initial representation spaces. To solve this problem, many methods have
been studied, which can be generally categorized into two types, i.e.,
representation learning-based CF methods and matching function learning-based
CF methods. Representation learning-based CF methods try to map users and items
into a common representation space. In this case, the higher similarity between
a user and an item in that space implies they match better. Matching function
learning-based CF methods try to directly learn the complex matching function
that maps user-item pairs to matching scores. Although both methods are well
developed, they suffer from two fundamental flaws, i.e., the limited
expressiveness of dot product and the weakness in capturing low-rank relations
respectively. To this end, we propose a general framework named DeepCF, short
for Deep Collaborative Filtering, to combine the strengths of the two types of
methods and overcome such flaws. Extensive experiments on four publicly
available datasets demonstrate the effectiveness of the proposed DeepCF
framework
Longitudinal optical conductivities in tilted Dirac bands
We report a unified theory based on linear response, for analyzing the
longitudinal optical conductivity (LOC) of materials with tilted Dirac cones.
Depending on the tilt parameter , the Dirac electrons have four phases,
untilted, type-I, type-II, and type-III; the Dirac dispersion can be isotropic
or anisotropic; the spatial dimension of the material can be one-, two-, or
three-dimensions. The interband LOCs and intraband LOCs in dimension (with
) are found to scale as to and
, respectively, where is the
frequency and the chemical potential. The interband LOCs always vanish in
one dimension due to lacking of extra spatial dimension. The angular dependence
of LOCs is found to characterize the band tilting, and the constant asymptotic
background values of LOC reflect features of the Dirac bands. The LOCs in the
anisotropic tilted Dirac cone can be connected to its isotropic counterpart by
a ratio that consists of Fermi velocities. The findings are valid for a great
many Dirac materials in the spatial dimensions of physical interests.Comment: 11 pages, 3 figure
Enhanced biosorption of Sb(III) onto living <i>Rhodotorula mucilaginosa</i>Â strain DJHN070401:optimization and mechanism
Advances in the Study of Magnesium Alloys and Their Use in Bone Implant Material
Magnesium and magnesium alloys have great application potential in the field of orthopaedics. Compared with traditional inorganic nonmetallic materials and medical polymer materials, magnesium alloys have many advantages, such as better strength, toughness, fatigue resistance, and easy processing. Its mechanical properties are suitable and controllable. It can meet the same elastic modulus, cell compatibility, and biodegradability as human cortical bone. There are also some drawbacks for biodegradability, as magnesium and its alloys, with their high degradation rate, can cause insufficient integrity of the mechanical properties. This paper summarises the research on magnesium and its magnesium alloy materials in the field of bone implantation, looking at what magnesium and its magnesium alloys are, the history of magnesium alloys in bone implant materials, the manufacturing of magnesium alloys, the mechanical properties of magnesium alloys, the bio-compatibility and clinical applications of magnesium alloys, the shortcomings, and the progress of research in recent years
A new stripe rust resistance gene transferred from Thinopyrum intermedium to hexaploid wheat (Triticum aestivum)
Wheat stripe rust (Puccinia striiforis f. sp. tritici) races CYR31 and CYR32, prevalent in China, are virulent to many wheat stripe rust resistance genes (Yr genes). To expand the availability of effective resistance to CYR31 and CYR32, stripe rust resistance was transferred from intermediate wheatgrass (Thinopyrum intermedium) to common wheat (Triticum aestivum). The susceptible wheat cultivar CM107 was crossed with amphiploid TAI7047, derived from the wide cross Taiyuan768/Thinopyrum intermedium//76(64). Two wheat lines originating from the cross, YU24 and YU25, were resistant to CYR31 and CYR32. Pedigree analysis showed that the resistance to stripe rust in YU24 and YU25 originated from intermediate wheatgrass. Genetic analyses indicated that the resistance to stripe rust is controlled by a single dominant gene. Allelic tests determined that the resistance gene(s) in YU24 and YU25 are identical. The new gene has temporarily been designated as YrYU25. SSR and RAPD analyses showed that YrYU25 was introduced by cryptic translocation into common wheat.Les races CYR31 et CYR32 de la rouille jaune du blé (Puccinia striiforis f. sp. tritici), trÚs répandues en Chine, sont virulentes pour plusieurs gÚnes de résistance à cette maladie (gÚnes Yr). Afin d'accroßtre la disponibilité d'une résistance efficace aux races CYR31 et CYR32, la résistance à la rouille jaune du blé a été transférée de l'agropyre intermédiaire (Thinopyrum intermedium) au blé tendre (Triticum aestivum). CM107, un cultivar de blé sensible, a été croisé avec l'amphiploïde AI7047 dérivé du croisement éloigné Taiyuan768/Thinopyrum intermedium//76(64). Deux lignées de blé provenant de ce croisement, soit YU24 et YU25, étaient résistantes aux races CYR31 et CYR32. Une analyse généalogique a démontré que la résistance à la rouille jaune du blé chez les lignées YU24 et YU25 provenait de l'agropyre intermédiaire. Des analyses génétiques ont indiqué que cette résistance était contrÎlée par un seul gÚne dominant. Des tests d'allélisme ont révélé que le(s) gÚne(s) de résistance dans les lignées YU24 et YU25 étaient identiques. Le nouveau gÚne a temporairement été nommé YrYU25. Des analyses SSR et RAPD ont démontré que le gÚne YrYU25 avait été introduit dans le blé tendre par translocation cryptique
QED contribution to the production of J/\psi+c\bar{c}+X at the Tevatron and LHC
We calculate \alpha^{2}\alpha_{s}^{2} order QED contribution to J/\psi
production in pp(\bar{p})\to J/\psi+c\bar{c} color-singlet process at the
Tevatron and LHC in the framework of non-relativistic QCD. The contribution of
the interference between the \alpha^{2}\alpha_{s}^{2} QED and \alpha_{s}^{4}
QCD is also taken into account. The J/\psi production associated with a charm
quark pair could be a measurable signal at hadron collider experiment. Our
calculations show that by including the QED contribution, the p_{t}
distribution is enhanced by a factor of 1.5 (1.9) at the Tevatron (LHC) at
p_{t}=50 (100) GeV. In addition, the polarization of J/\psi turns from
unpolarized in all region to increasingly transverse when p_{t} becomes larger.Comment: 14 pages, 6 figures, version accepted for publication in Phys Rev
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