47,446 research outputs found
Exact States in Waveguides With Periodically Modulated Nonlinearity
We introduce a one-dimensional model based on the nonlinear
Schrodinger/Gross-Pitaevskii equation where the local nonlinearity is subject
to spatially periodic modulation in terms of the Jacobi dn function, with three
free parameters including the period, amplitude, and internal form-factor. An
exact periodic solution is found for each set of parameters and, which is more
important for physical realizations, we solve the inverse problem and predict
the period and amplitude of the modulation that yields a particular exact
spatially periodic state. Numerical stability analysis demonstrates that the
periodic states become modulationally unstable for large periods, and regain
stability in the limit of an infinite period, which corresponds to a bright
soliton pinned to a localized nonlinearity-modulation pattern. Exact
dark-bright soliton complex in a coupled system with a localized modulation
structure is also briefly considered . The system can be realized in planar
optical waveguides and cigar-shaped atomic Bose-Einstein condensates.Comment: EPL, in pres
Capitalist pigs: Governmentality, subjectivities, and the regulation of pig farming in colonial Hong Kong, 1950–1970
This is the author accepted manuscript. The final version is available from SAGE Publications via the DOI in this record.This paper analyses the philanthropic governmentality of the Hong Kong colonial government during the Farm Improvement Program (1950–70), focusing on the utilization of pigs, interest-free loans, and the spatial constitution of pig farming as technologies to transform refugee farmers into ‘productive workers’. This research has three primary objectives: to (1) elucidate how the production of knowledge and governing technologies, including the spatial design of livestock production, facilitated the disciplining of pig farmers in a colonial context; (2) expand Foucauldian governmentality analysis into the realm of the regulatory mechanisms of food production systems by documenting how philanthropic pig donations, lending programmes, and the distribution of material benefits promoted capitalist pig production; and (3) demonstrate how technologies – specifically the social construction of pigs and the spatial constitution of pig farming practices – moulded the subjectivities of colonial pig farmers. Empirical analysis is based on archival research and in-depth interviews with 19 pig farmers and two pig farmers’ association leaders. We identify the provision of free pigs and pigsties, the demonstration of new spatial pig-raising practices, and the establishment of interest-free lending systems as the major technologies of governance employed under the Farm Improvement Program. Through these technologies refugee farmers from mainland China learned and internalized concepts of efficiency, productivity, farm management, and self-help. The technologies of the Farm Improvement Program were not just philanthropic activities, they were political tactics to confront the penetration of communism into the colony by changing the practices, productivity, and subjectivities of refugee farmers
Evolution Of Feeding Shapes Swimming Kinematics Of Barnacle Naupliar Larvae: A Comparison Between Trophic Modes
A central goal in evolutionary biology is connecting morphological features with ecological functions. For marine invertebrate larvae, appendage movement determines locomotion, feeding, and predator avoidance ability. Barnacle larvae are morphologically diverse, and the morphology of non-feeding lecithotrophic nauplii are distinct from those that are planktotrophic. Lecithotrophic larvae have a more globular body shape and simplified appendages when compared with planktotrophs. However, little is known about whether and how such morphological changes affect kinematics, hydrodynamics, and ecological functions. Here, we compared the nauplii kinematics and hydrodynamics of a lecithotrophic Rhizocephalan species, Polyascus planus, against that of the planktotrophic nauplii of an intertidal barnacle, Tetraclita japonica. High-speed, micro-particle image velocimetry analysis showed that the Polyascus nauplii swam faster and had higher amplitude and more synchronous appendage beating than the Tetraclita nauplii. This fast swimming was accompanied by a faster attenuation of induced flow with distance, suggesting reduced predation risk. Tetraclita nauplii had more efficient per beat cycles with less backward displacement during the recovery stroke. This “anchoring effect” resulted from the anti-phase beating of appendages. This movement, together with a high-drag body form, likely helps direct the suction flow toward the ventral food capturing area. In sum, the tradeoff between swimming speed and predation risks may have been an important factor in the evolution of the observed larval forms
Statistical variability in implant-free quantum-well MOSFETs with InGaAs and Ge: a comparative 3D simulation study
Introduction of high mobility channel materials including III-Vs and Ge into future CMOS generations offer the
potential for enhanced transport properties compared to Si. The Implant Free Quantum Well (IFQW) architecture
offers an attractive design to introduce these materials, providing excellent electrostatic integrity. Statistical variability introduced by the discreteness of charge and granularity of matter has become a key factor for current and future generations of MOSFETs and in this work numerical simulations are used to critically assess the statistical
variability in IFQW transistors and compare results with equivalent conventional Si ‘bulk’ MOSFETs
A Tail’s Tale: Biomechanical Roles Of Dorsal Thoracic Spine Of Barnacle Nauplii
Many marine invertebrates have complex life histories that begin with a planktonic larval stage. Similar to other plankton, these larval invertebrates often possess protruding body extensions, but their function beyond predator deterrence is not well-documented. For example, the planktonic nauplii of crustaceans have spines. Using the epibiotic pedunculate barnacle Octolasmis spp., we investigated how the dorsal thoracic spine affects swimming and fluid disturbance by comparing nauplii with their spines partially removed against those with intact spines. Our motion analysis showed that amputated Octolasmis spp. swam slower, in jerkier trajectories, and were less efficient per stroke cycle than those with intact spines. Amputees showed alterations in limb beat pattern: larger beat amplitude, increased phase lag, and reduced contralateral symmetry. These changes might partially help increase propulsive force generation and streamline the flow, but were insufficient to restore full function. Particle image velocimetry further showed that amputees had a larger relative area of influence, implying elevated risk by rheotactic predator. Body extensions and their interactions with limb motion play important biomechanical roles in shaping larval performance, which likely influences the evolution of form
Topological dilaton black holes
In four-dimensional spacetime, when the two-sphere of black hole event
horizons is replaced by a two-dimensional hypersurface with zero or negative
constant curvature, the black hole is referred to as a topological black hole.
In this paper we present some exact topological black hole solutions in the
Einstein-Maxwell-dilaton theory with a Liouville-type dilaton potential.Comment: 8 pages, Revtex, no figure
Reconfigurable self-sufficient traps for ultracold atoms based on a superconducting square
We report on the trapping of ultracold atoms in the magnetic field formed
entirely by persistent supercurrents induced in a thin film type-II
superconducting square. The supercurrents are carried by vortices induced in
the 2D structure by applying two magnetic field pulses of varying amplitude
perpendicular to its surface. This results in a self-sufficient quadrupole trap
that does not require any externally applied fields. We investigate the
trapping parameters for different supercurrent distributions. Furthermore, to
demonstrate possible applications of these types of supercurrent traps we show
how a central quadrupole trap can be split into four traps by the use of a bias
field.Comment: 5 pages, 7 figure
Charged Black Cosmic String
Global U(1) strings with cylindrical symmetry are studied in anti-de Sitter
spacetime. According as the magnitude of negative cosmological constant, they
form regular global cosmic strings, extremal black cosmic strings and charged
black cosmic strings, but no curvature singularity is involved. The
relationship between the topological charge of a neutral global string and the
black hole charge is clarified by duality transformation. Physical relevance as
straight string is briefly discussed.Comment: ll pages, LaTe
Exact Black Hole and Cosmological Solutions in a Two-Dimensional Dilaton-Spectator Theory of Gravity
Exact black hole and cosmological solutions are obtained for a special
two-dimensional dilaton-spectator () theory of gravity. We show how
in this context any desired spacetime behaviour can be determined by an
appropriate choice of a dilaton potential function and a ``coupling
function'' in the action. We illustrate several black hole solutions
as examples. In particular, asymptotically flat double- and multiple- horizon
black hole solutions are obtained. One solution bears an interesting
resemblance to the string-theoretic black hole and contains the same
thermodynamic properties; another resembles the Reissner-Nordstrom
solution. We find two characteristic features of all the black hole solutions.
First the coupling constants in must be set equal to constants of
integration (typically the mass). Second, the spectator field and its
derivative both diverge at any event horizon. A test particle with
``spectator charge" ({\it i.e.} one coupled either to or ),
will therefore encounter an infinite tidal force at the horizon or an
``infinite potential barrier'' located outside the horizon respectively. We
also compute the Hawking temperature and entropy for our solutions. In
cosmology, two non-singular solutions which resemble two exact solutions
in string-motivated cosmology are obtained. In addition, we construct a
singular model which describes the standard non-inflationary big bang
cosmology (). Motivated by the
similaritiesbetween and gravitational field equations in
cosmology, we briefly discuss a special dilaton-spectator action
constructed from the bosonic part of the low energy heterotic string action andComment: 34 pgs. Plain Tex, revised version contains some clarifying comments
concerning the relationship between the constants of integration and the
coupling constants
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