622 research outputs found
Coexistence of single-mode and multi-longitudinal mode emission in the ring laser model
A homogeneously broadened unidirectonal ring laser can emit in several
longitudinal modes for large enough pump and cavity length because of Rabi
splitting induced gain. This is the so called Risken-Nummedal-Graham-Haken
(RNGH) instability. We investigate numerically the properties of the multi-mode
solution. We show that this solution can coexist with the single-mode one, and
its stability domain can extend to pump values smaller than the critical pump
of the RNGH instability. Morevoer, we show that the multi-mode solution for
large pump values is affected by two different instabilities: a pitchfork
bifurcation, which preserves phase-locking, and a Hopf bifurcation, which
destroys it.Comment: 14 pages, 7 figure
Stability of Attractive Bose-Einstein Condensates in a Periodic Potential
Using a standing light wave trap, a stable quasi-one-dimensional attractive
dilute-gas Bose-Einstein condensate can be realized. In a mean-field
approximation, this phenomenon is modeled by the cubic nonlinear Schr\"odinger
equation with attractive nonlinearity and an elliptic function potential of
which a standing light wave is a special case. New families of stationary
solutions are presented. Some of these solutions have neither an analog in the
linear Schr\"odinger equation nor in the integrable nonlinear Schr\"odinger
equation. Their stability is examined using analytic and numerical methods.
Trivial-phase solutions are experimentally stable provided they have nodes and
their density is localized in the troughs of the potential. Stable
time-periodic solutions are also examined.Comment: 12 pages, 18 figure
Industrial applications of accelerator-based infrared sources: analysis using infrared microspectroscopy
Infrared Microspectroscopy, using a globar source, is now widely employed in the industrial environment, for the analysis of various materials. Since synchrotron radiation is a much brighter source, an enhancement of an order of magnitude in lateral resolution can be achieved. Thus, the combination of IR microspectroscopy and synchrotron radiation provides a powerful tool enabling sample regions only few microns size to be studied. This opens up the potential for analyzing small particles. Some examples for hair, bitumen and polymer are presented
Dynamics of a large extra dimension inspired hybrid inflation model
In low scale quantum gravity scenarios the fundamental scale of nature can be
as low as TeV, in order to address the naturalness of the electroweak scale. A
number of difficulties arise in constructing specific models; stabilisation of
the radius of the extra dimensions, avoidance of overproduction of Kaluza Klein
modes, achieving successful baryogenesis and production of a close to
scale-invariant spectrum of density perturbations with the correct amplitude.
We examine in detail the dynamics, including radion stabilisation, of a hybrid
inflation model that has been proposed in order to address these difficulties,
where the inflaton is a gauge singlet residing in the bulk. We find that for a
low fundamental scale the phase transition, which in standard four dimensional
hybrid models usually ends inflation, is slow and there is second phase of
inflation lasting for a large number of e-foldings. The density perturbations
on cosmologically interesting scales exit the Hubble radius during this second
phase of inflation, and we find that their amplitude is far smaller than is
required. We find that the duration of the second phase of inflation can be
short, so that cosmologically interesting scales exit the Hubble radius prior
to the phase transition, and the density perturbations have the correct
amplitude, only if the fundamental scale takes an intermediate value. Finally
we comment briefly on the implications of an intermediate fundamental scale for
the production of primordial black holes and baryogenesis.Comment: 9 pages, 2 figures version to appear in Phys. Rev. D, additional
references and minor changes to discussio
ISML: an interface specification meta-language
In this paper we present an abstract metaphor model situated within a model-based user interface framework. The inclusion of metaphors in graphical user interfaces is a well established, but mostly craft-based strategy to design. A substantial body of notations and tools can be found within the model-based user interface design literature, however an explicit treatment of metaphor and its mappings to other design views has yet to be addressed. We introduce the Interface Specification Meta-Language (ISML) framework and demonstrate its use in comparing the semantic and syntactic features of an interactive system. Challenges facing this research are outlined and further work proposed
Chemical imaging of living cells by synchrotron infrared microspectrometry
Chemical mapping of proteins and lipids inside a single living cell and at a resolution of a few microns, has been performed using synchroton infrared microspectrometry. Modifications of the chemical distributions upon mitosis and necrosis has been investigated
Constraints on dark matter particles charged under a hidden gauge group from primordial black holes
In order to accommodate increasingly tighter observational constraints on
dark matter, several models have been proposed recently in which dark matter
particles are charged under some hidden gauge group. Hidden gauge charges are
invisible for the standard model particles, hence such scenarios are very
difficult to constrain directly. However black holes are sensitive to all gauge
charges, whether they belong to the standard model or not. Here, we examine the
constraints on the possible values of the dark matter particle mass and hidden
gauge charge from the evolution of primordial black holes. We find that the
existence of the primordial black holes with reasonable mass is incompatible
with dark matter particles whose charge to mass ratio is of the order of one.
For dark matter particles whose charge to mass ratio is much less than one, we
are able to exclude only heavy dark matter in the mass range of 10^(11) GeV -
10^(16) GeV. Finally, for dark matter particles whose charge to mass ratio is
much greater than one, there are no useful limits coming from primordial black
holes.Comment: accepted for publication in JCA
Bose-Einstein condensates in a one-dimensional double square well: Analytical solutions of the Nonlinear Schr\"odinger equation and tunneling splittings
We present a representative set of analytic stationary state solutions of the
Nonlinear Schr\"odinger equation for a symmetric double square well potential
for both attractive and repulsive nonlinearity. In addition to the usual
symmetry preserving even and odd states, nonlinearity introduces quite exotic
symmetry breaking solutions - among them are trains of solitons with different
number and sizes of density lumps in the two wells. We use the symmetry
breaking localized solutions to form macroscopic quantum superpositions states
and explore a simple model for the exponentially small tunneling splitting.Comment: 11 pages, 11 figures, revised version, typos and references correcte
Superfield T-duality rules
A geometric treatment of T-duality as an operation which acts on differential
forms in superspace allows us to derive the complete set of T-duality
transformation rules which relate the superfield potentials of D=10 type IIA
supergravity with those of type IIB supergravity including Ramond-Ramond
superfield potentials and fermionic supervielbeins. We show that these rules
are consistent with the superspace supergravity constraints.Comment: 24 pages, latex, no figures. V2 misprints corrected. V3. One
reference ([30]) and a comment on it ('Notice added') on p. 19 adde
Solitons in Triangular and Honeycomb Dynamical Lattices with the Cubic Nonlinearity
We study the existence and stability of localized states in the discrete
nonlinear Schr{\"o}dinger equation (DNLS) on two-dimensional non-square
lattices. The model includes both the nearest-neighbor and long-range
interactions. For the fundamental strongly localized soliton, the results
depend on the coordination number, i.e., on the particular type of the lattice.
The long-range interactions additionally destabilize the discrete soliton, or
make it more stable, if the sign of the interaction is, respectively, the same
as or opposite to the sign of the short-range interaction. We also explore more
complicated solutions, such as twisted localized modes (TLM's) and solutions
carrying multiple topological charge (vortices) that are specific to the
triangular and honeycomb lattices. In the cases when such vortices are
unstable, direct simulations demonstrate that they turn into zero-vorticity
fundamental solitons.Comment: 17 pages, 13 figures, Phys. Rev.
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