2,653 research outputs found
Steering far-field spin-dependent splitting of light by inhomogeneous anisotropic media
An inhomogeneous anisotropic medium with specific structure geometry can
apply the tunable spin-dependent geometrical phase to the light passing through
the medium, and thus can be used to steer the spin-dependent splitting (SDS) of
light. In this paper, we exemplify this inference by the q plate, an
inhomogeneous anisotropic medium. It is demonstrated that when a linearly
polarized light beam normally passes through a q plate, k-space SDS first
occurs, and then the real-space SDS in the far-field focal plane of a
converging lens is distinguishable. Interestingly, the SDS, described by the
normalized Stokes parameter S3 shows a multilobe and rotatable splitting
pattern with rotational symmetry. Further, by tailoring the structure geometry
of the q plate and/or the incident polarization angle of light, the lobe number
and the rotation angle both are tunable. Our result suggests that the q plate
can serve as a potential device for manipulating the photon spin states and
enable applications such as in nano-optics and quantum information.Comment: 5 pages, 5 figure
Operational considerations on the stability of colliding beams
While well studied in the absence of beam-beam and while colliding head-on,
the stability of the LHC beams can be very critical in intermediate steps.
During the squeeze, the long-range beam-beam interaction becomes a critical
component of the beam's dynamics. Also, while the transverse separation at the
interaction points is collapsed, the beam-beam forces change drastically,
possibly deteriorating the beam's stability. Finally, during luminosity
production, the configuration of the LHC in 2012 included few bunches without
head-on collision in any of the interaction points having different stability
properties. Stability diagrams are being evaluated numerically in these
configurations in an attempt to explain instabilities observed in these phases
during the 2012 proton run of the LHC.Comment: 5 pages, contribution to the ICFA Mini-Workshop on Beam-Beam Effects
in Hadron Colliders, CERN, Geneva, Switzerland, 18-22 Mar 201
Does the Principle of Compositionality Explain Productivity? For a Pluralist View of the Role of Formal Languages as Models
One of the main motivations for having a compositional semantics is the account of the productivity of natural languages. Formal languages are often part of the account of productivity, i.e., of how beings with finite capaci- ties are able to produce and understand a potentially infinite number of sen- tences, by offering a model of this process. This account of productivity con- sists in the generation of proofs in a formal system, that is taken to represent the way speakers grasp the meaning of an indefinite number of sentences. The informational basis is restricted to what is represented in the lexicon. This constraint is considered as a requirement for the account of productivity, or at least of an important feature of productivity, namely, that we can grasp auto- matically the meaning of a huge number of complex expressions, far beyond what can be memorized. However, empirical results in psycholinguistics, and especially particular patterns of ERP, show that the brain integrates informa- tion of different sources very fast, without any felt effort on the part of the speaker. This shows that formal procedures do not explain productivity. How- ever, formal models are still useful in the account of how we get at the seman- tic value of a complex expression, once we have the meanings of its parts, even if there is no formal explanation of how we get at those meanings. A practice-oriented view of modeling gives an adequate interpretation of this re- sult: formal compositional semantics may be a useful model for some ex- planatory purposes concerning natural languages, without being a good model for dealing with other explananda
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