4,726 research outputs found
Renormalization-group and numerical analysis of a noisy Kuramoto-Sivashinsky equation in 1+1 dimensions
The long-wavelength properties of a noisy Kuramoto-Sivashinsky (KS) equation
in 1+1 dimensions are investigated by use of the dynamic renormalization group
(RG) and direct numerical simulations. It is shown that the noisy KS equation
is in the same universality class as the Kardar-Parisi-Zhang (KPZ) equation in
the sense that they have scale invariant solutions with the same scaling
exponents in the long-wavelength limit. The RG analysis reveals that the RG
flow for the parameters of the noisy KS equation rapidly approach the KPZ fixed
point with increasing the strength of the noise. This is supplemented by the
numerical simulations of the KS equation with a stochastic noise, in which the
scaling behavior of the KPZ equation can be easily observed even in the
moderate system size and time.Comment: 12pages, 7figure
Interspecific differences in the larval performance of Pieris butterflies (Lepidoptera: Pieridae) are associated with differences in the glucosinolate profiles of host plants
The tremendous diversity of plants and herbivores has arisen from a coevolutionary relationship characterized by plant defense and herbivore counter adaptation. Pierid butterfly species feed on Brassicales plants that produce glucosinolates as a chemical deterrent against herbivory. In turn, the larvae of pierids have nitrile specifier proteins (NSPs) that are expressed in their gut and disarm glucosinolates. Pierid butterflies are known to have diversified in response to glucosinolate diversification in Brassicales. Therefore, each pierid species is expected to have a spectrum of host plants characterized by specific glucosinolate profiles. In this study, we tested whether the larval performance of different Pieris species, a genus in Pieridae (Lepidoptera: Pieridae), was associated with plant defense traits of putative host plants. We conducted feeding assays using larvae of three Pieris species and 10 species of the Brassicaceae family possessing different leaf physical traits and glucosinolate profile measurements. The larvae of Pieris rapae responded differently in the feeding assays compared with the other two Pieris species. This difference was associated with differences in glucosinolate profiles but not with variations in physical traits of the host plants. This result suggests that individual Pieris species are adapted to a subset of glucosinolate profiles within the Brassicaceae. Our results support the idea that the host ranges of Pieris species depend on larval responses to glucosinolate diversification in the host species, supporting the hypothesis of coevolution between butterflies and host plants mediated by the chemical arms race
Vortex lattice for a holographic superconductor
We investigate the vortex lattice solution in a (2+1)-dimensional holographic
model of superconductors constructed from a charged scalar condensate. The
solution is obtained perturbatively near the second-order phase transition and
is a holographic realization of the Abrikosov lattice. Below a critical value
of magnetic field, the solution has a lower free energy than the normal state.
Both the free energy density and the superconducting current are expressed by
nonlocal functions, but they reduce to the expressions in the Ginzburg-Landau
(GL) theory at long wavelength. As a result, a triangular lattice becomes the
most favorable solution thermodynamically as in the GL theory of type II
superconductors.Comment: v2: minor changes, references added; 11 pages, 2 figures: version to
appear in PR
Mirror effect induced by the dilaton field on the Hawking radiation
We discuss the string creation in the near-extremal NS1 black string
solution. The string creation is described by an effective field equation
derived from a fundamental string action coupled to the dilaton field in a
conformally invariant manner. In the non-critical string model the dilaton
field causes a timelike mirror surface outside the horizon when the size of the
black string is comparable to the Planck scale. Since the fundamental strings
are reflected by the mirror surface, the negative energy flux does not
propagate across the surface. This means that the evaporation stops just before
the naked singularity of the extremal black string appears even though the
surface gravity is non-zero in the extremal limit.Comment: 15 page
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A classroom deployment of a haptic system for learning cell biology
The use of haptic systems in the classroom for enhancing science education is an underexplored area. In the education literature, it has been reported that certain concepts in science education are difficult for students to grasp and, as a result, misconceptions can be formed in the students' knowledge. We conducted a study with 62 Year 8 (typically 12-13 years old) students who used a haptic application to study cell biology, specifically the concept of diffusion across a cell membrane. The preliminary analysis of the feedback from the students suggests opportunities for haptic applications to enhance their learning, and also highlights a number of points to consider in the design of the application, including the choice of haptic interface and the design of the virtual environment
Theory for Magnetic Anisotropy of Field-Induced Insulator-to-Metal Transition in Cubic Kondo Insulator YbB_{12}
Magnetization and energy gap of Kondo insulator YbB_{12} are calculated
theoretically based on the previously proposed tight-binding model composed of
Yb 5d and 4f orbitals. It is found that magnetization
curves are almost isotropic, naturally expected from the cubic symmetry, but
that the gap-closing field has an anisotropy: the gap closes faster for the
field in (100) direction than in (110) and (111) directions, in accord with the
experiments. This is qualitatively understood by considering the maximal
eigenvalues of the total angular momentum operators projected on each direction
of the magnetic field. But the numerical calculation based on the band model
yields better agreement with the experiment.Comment: 4 pages, 4 figures, to appear in J. Phys. Soc. Jp
On two pieces of folklore in the AdS/CFT duality
In the AdS/CFT duality, it is often said that a local symmetry in a bulk
theory corresponds to a global symmetry in the corresponding boundary theory,
but the global symmetry can become local when one couples with an external
source. As a result, the GKP-Witten relation gives a response function instead
of a Green function. We explore this point in details using the example of
holographic superconductors. We point out that these points play a crucial role
to interpret the holographic London equation properly.Comment: 11 pages, ReVTeX4.1; v2: added discussio
Carbon in Spiral Galaxies from Hubble Space Telescope Spectroscopy
We present measurements of the gas-phase C/O abundance ratio in six H II
regions in the spiral galaxies M101 and NGC 2403, based on ultraviolet
spectroscopy using the Faint Object Spectrograph on the Hubble Space Telescope.
The C/O ratios increase systematically with O/H in both galaxies, from log C/O
approximately -0.8 at log O/H = -4.0 to log C/O approx. -0.1 at log O/H = -3.4.
C/N shows no correlation with O/H. The rate of increase of C/O is somewhat
uncertain because of uncertainty as to the appropriate UV reddening law, and
uncertainty in the metallicity dependence on grain depletions. However, the
trend of increasing C/O with O/H is clear, confirming and extending the trend
in C/O indicated previously from observations of irregular galaxies. Our data
indicate that the radial gradients in C/H across spiral galaxies are steeper
than the gradients in O/H. Comparing the data to chemical evolution models for
spiral galaxies shows that models in which the massive star yields do not vary
with metallicity predict radial C/O gradients that are much flatter than the
observed gradients. The most likely hypothesis at present is that stellar winds
in massive stars have an important effect on the yields and thus on the
evolution of carbon and oxygen abundances. C/O and N/O abundance ratios in the
outer disks of spirals determined to date are very similar to those in dwarf
irregular galaxies. This implies that the outer disks of spirals have average
stellar population ages much younger than the inner disks.Comment: 38 pages, 9 postscript figures, uses aaspp4.sty. Accepted for
publication in The Astrophysical Journa
Strange filamentary structures ("fireballs") around a merger galaxy in the Coma cluster of galaxies
We found an unusual complex of narrow blue filaments, bright blue knots, and
H-alpha emitting filaments and clouds, which morphologically resembled a
complex of ``fireballs,'' extending up to 80 kpc south from an E+A galaxy RB199
in the Coma cluster. The galaxy has a highly disturbed morphology indicative of
a galaxy--galaxy merger remnant. The narrow blue filaments extend in straight
shapes toward the south from the galaxy, and several bright blue knots are
located at the southern ends of the filaments. The Rc band absolute magnitudes,
half light radii and estimated masses of the bright knots are -12 - -13 mag,
200 - 300 pc and 10^6-7 Msolar, respectively. Long, narrow H-alpha emitting
filaments are connected at the south edge of the knots. The average color of
the fireballs is B - Rc = 0.5, which is bluer than RB199 (B - R = 0.99),
suggesting that most of the stars in the fireballs were formed within several
times 10^8 yr. The narrow blue filaments exhibit almost no H-alpha emission.
Strong H-alpha and UV emission appear in the bright knots. These
characteristics indicate that star formation recently ceased in the blue
filaments and now continues in the bright knots. The gas stripped by some
mechanism from the disk of RB199 may be traveling in the intergalactic space,
forming stars left along its trajectory. The most plausible fireball formation
mechanism is ram pressure stripping by high-speed collision between the galaxy
and the hot intra-cluster medium. The fireballs may be a snapshot of diffuse
intra-cluster population formation, or halo star population formation in a
cluster galaxy.Comment: 13 pages, 14 figures, submitted to Ap
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