43 research outputs found
Multifractals Competing with Solitons on Fibonacci Optical Lattice
We study the stationary states for the nonlinear Schr\"odinger equation on
the Fibonacci lattice which is expected to be realized by Bose-Einstein
condensates loaded into an optical lattice. When the model does not have a
nonlinear term, the wavefunctions and the spectrum are known to show fractal
structures. Such wavefunctions are called critical. We present a phase diagram
of the energy spectrum for varying the nonlinearity. It consists of three
portions, a forbidden region, the spectrum of critical states, and the spectrum
of stationary solitons. We show that the energy spectrum of critical states
remains intact irrespective of the nonlinearity in the sea of a large number of
stationary solitons.Comment: 5 pages, 4 figures, major revision, references adde
Técnica do gás traçador SF6 para medição de campo do metano ruminal em bovinos: adaptações para o Brasil.
bitstream/CPPSE/15523/1/PROCIDOC39OP2004.00219.pd
Robust optical delay lines via topological protection
Phenomena associated with topological properties of physical systems are
naturally robust against perturbations. This robustness is exemplified by
quantized conductance and edge state transport in the quantum Hall and quantum
spin Hall effects. Here we show how exploiting topological properties of
optical systems can be used to implement robust photonic devices. We
demonstrate how quantum spin Hall Hamiltonians can be created with linear
optical elements using a network of coupled resonator optical waveguides (CROW)
in two dimensions. We find that key features of quantum Hall systems, including
the characteristic Hofstadter butterfly and robust edge state transport, can be
obtained in such systems. As a specific application, we show that the
topological protection can be used to dramatically improve the performance of
optical delay lines and to overcome limitations related to disorder in photonic
technologies.Comment: 9 pages, 5 figures + 12 pages of supplementary informatio
Toward a geography of black internationalism: Bayard Rustin, nonviolence and the promise of Africa
This article charts the trip made by civil rights leader Bayard Rustin to West Africa in 1952, and examines the unpublished ‘Africa Program’ which he subsequently presented to leading American pacifists. I situate Rustin’s writings within the burgeoning literature on black internationalism which, despite its clear geographical registers, geographers themselves have as yet made only a modest contribution towards. The article argues that within this literature there remains a tendency to romanticize cross-cultural connections in lieu of critically interrogating their basic, and often competing, claims. I argue that closer attention to the geographies of black internationalism, however, allows us to shape a more diverse and practiced sense of internationalist encounter and exchange. The article reconstructs the multiplicity of Rustin’s black internationalist geographies which drew eclectically from a range of Pan-African, American and pacifist traditions. Though each of these was profoundly racialized, they conceptualized race in distinctive ways and thereby had differing understandings of what constituted the international as a geographical arena. By blending these forms of internationalism Rustin was able to promote a particular model of civil rights which was characteristically internationalist in outlook, nonviolent in principle and institutional in composition; a model which in selective and uneven ways continues to shape our understanding of the period
Ultra-low-power hybrid light-matter solitons.
New functionalities in nonlinear optics will require systems with giant optical nonlinearity as well as compatibility with photonic circuit fabrication techniques. Here we introduce a platform based on strong light-matter coupling between waveguide photons and quantum-well excitons. On a sub-millimetre length scale we generate picosecond bright temporal solitons at a pulse energy of only 0.5 pJ. From this we deduce a nonlinear refractive index three orders of magnitude larger than in any other ultrafast system. We study both temporal and spatio-temporal nonlinear effects and observe dark-bright spatio-temporal polariton solitons. Theoretical modelling of soliton formation in the strongly coupled system confirms the experimental observations. These results show the promise of our system as a high speed, low power, integrated platform for physics and devices based on strong interactions between photons
Contextualising Apartheid at the End of Empire: Repression, ‘Development’ and the Bantustans
This article examines the global dynamics of late colonialism and how these informed
South African apartheid. More specifically, it locates the programmes of mass
relocation and bantustan ‘self-government’ that characterised apartheid after 1959 in
relation to three key dimensions. Firstly, the article explores the global circulation of
idioms of ‘development’ and trusteeship in the first half of the twentieth century and its
significance in shaping segregationist policy; secondly, it situates bantustan ‘selfgovernment’
in relation to the history of decolonisation and the partitions and
federations that emerged as late colonial solutions; and, thirdly, it locates the
tightening of rural village planning in the bantustans after 1960 in relation to the
elaboration of anti-colonial liberation struggles, repressive southern African settler
politics and the Cold War. It argues that, far from developing policies that were at odds
with the global ‘wind of change’, South African apartheid during the 1960s and 1970s
reflected much that was characteristic about late colonial strategy
Conical Diffraction And Gap Solitons In Honeycomb Photonic Lattices
We predict and present the first observation of conical diffraction arising from k-space singularities in the band-structure of a periodic potential. The experiments are carried out in honeycomb lattices, where we also generate honeycomb gap-solitons . © 2007 Optical Society of America
Conical Diffraction And Gap Solitons In Honeycomb Photonic Lattices
We predict and present the first observation of conical diffraction arising from k-space singularities in the band-structure of a periodic potential. The experiments are carried out in honeycomb lattices, where we also generate honeycomb gap-solitons . © 2007 Optical Society of America
Lattice Surface Solitons
It is theoretically shown that nonlinear surface-waves are possible in optical lattices. Such solitons can exist at the interface between two different semi-infinite 1D waveguide arrays and also at the boundaries of a 2D lattice. © 2006 Optical Society of America