4,159 research outputs found
Higher Order Modulation Equations for a Boussinesq Equation
In order to investigate corrections to the common KdV approximation to long
waves, we derive modulation equations for the evolution of long wavelength
initial data for a Boussinesq equation. The equations governing the corrections
to the KdV approximation are explicitly solvable and we prove estimates showing
that they do indeed give a significantly better approximation than the KdV
equation alone. We also present the results of numerical experiments which show
that the error estimates we derive are essentially optimal
Decoupled and unidirectional asymptotic models for the propagation of internal waves
We study the relevance of various scalar equations, such as inviscid
Burgers', Korteweg-de Vries (KdV), extended KdV, and higher order equations (of
Camassa-Holm type), as asymptotic models for the propagation of internal waves
in a two-fluid system. These scalar evolution equations may be justified with
two approaches. The first method consists in approximating the flow with two
decoupled, counterpropagating waves, each one satisfying such an equation. One
also recovers homologous equations when focusing on a given direction of
propagation, and seeking unidirectional approximate solutions. This second
justification is more restrictive as for the admissible initial data, but
yields greater accuracy. Additionally, we present several new coupled
asymptotic models: a Green-Naghdi type model, its simplified version in the
so-called Camassa-Holm regime, and a weakly decoupled model. All of the models
are rigorously justified in the sense of consistency
Orbital Ordering in ferromagnetic Lu2V2O7
We have observed the orbital ordering in the ferromagnetic Mott-insulator
Lu2V2O7 by the polarized neutron diffraction technique. The orbital ordering
pattern determined from the observed magnetic form factors can be explained in
terms of a linear combination of wave functions |yz>, |zx> and |xy>; |0> =
(1/3)^(1/2) |xy> + (1/3)^(1/2)|yz> + (1/3)^(1/2) |zx> which is proportional to
|(x + y + z)^2 - r^2>; where each orbital is extended toward the center-of-mass
of the V tetrahedron. We discuss the stability of the ferromagnetic Lu2V2O7,
using a Hubbard Hamiltonian with these three orbitals.Comment: 17pages. to be published in J. Phys. Soc. Jpn. 74 (2005
All Coronal Loops are the Same: Evidence to the Contrary
The 1998 April 20 spectral line data from the Coronal Diagnostics
Spectrometer (CDS) on the {\it Solar and Heliospheric Observatory} (\SOHO)
shows a coronal loop on the solar limb. Our original analysis of these data
showed that the plasma was multi-thermal, both along the length of the loop and
along the line of sight. However, more recent results by other authors indicate
that background subtraction might change these conclusions, so we consider the
effect of background subtraction on our analysis. We show Emission Measure (EM)
Loci plots of three representative pixels: loop apex, upper leg, and lower leg.
Comparisons of the original and background-subtracted intensities show that the
EM Loci are more tightly clustered after background subtraction, but that the
plasma is still not well represented by an isothermal model. Our results taken
together with those of other authors indicate that a variety of temperature
structures may be present within loops.Comment: Accepted for publication in ApJ Letter
Coronal Temperature Diagnostic Capability of the Hinode/X-Ray Telescope Based on Self-Consistent Calibration
The X-Ray Telescope (XRT) onboard the Hinode satellite is an X-ray imager
that observes the solar corona with unprecedentedly high angular resolution
(consistent with its 1" pixel size). XRT has nine X-ray analysis filters with
different temperature responses. One of the most significant scientific
features of this telescope is its capability of diagnosing coronal temperatures
from less than 1 MK to more than 10 MK, which has never been accomplished
before. To make full use of this capability, accurate calibration of the
coronal temperature response of XRT is indispensable and is presented in this
article. The effect of on-orbit contamination is also taken into account in the
calibration. On the basis of our calibration results, we review the
coronal-temperature-diagnostic capability of XRT
Energy Spectra of Quantum Turbulence: Large-scale Simulation and Modeling
In simulation of quantum turbulence within the Gross-Pitaevskii
equation we demonstrate that the large scale motions have a classical
Kolmogorov-1941 energy spectrum E(k) ~ k^{-5/3}, followed by an energy
accumulation with E(k) ~ const at k about the reciprocal mean intervortex
distance. This behavior was predicted by the L'vov-Nazarenko-Rudenko bottleneck
model of gradual eddy-wave crossover [J. Low Temp. Phys. 153, 140-161 (2008)],
further developed in the paper.Comment: (re)submitted to PRB: 5.5 pages, 4 figure
Family firm internationalization: Past research and an agenda for the future
Although the study of family firm internationalization has generated considerable scholarly attention, existing research has offered varied and at times incompatible findings on how family ownership and management shape internationalization. To improve our understanding of family firm internationalization, we systematically review 220 conceptual and empirical studies published over the past three decades, structuring our comprehensive overview of this field according to seven core international business (IB) themes. We assess the literature and propose directions for future research by developing an integrative framework of family firm internationalization that links IB theory with conceptual perspectives used in the reviewed body of work. We propose a research agenda that advocates a cross-disciplinary, multi-theoretic, and cross-level approach to studying family firm internationalization. We conclude that family firm internationalization research has the potential to contribute valuable insights to IB scholarship by increasing attention to conceptual and methodological issues, including micro-level affective motivations, background social institutions, temporal perspectives, and multi-level analyses
Biogeochemistry and geomicrobiology of cold-water coral carbonate mounds - lessons learned from IODP Expedition 307
Large mound structures associated with cold-water coral ecosystems commonly occur on the slopes of continental margins, for instance, west of Ireland in the Porcupine Seabight, the Gulf of Cadiz or the Straits of Florida. In the Porcupine Seabight over 1500 mounds of up to 5 km in diameter and 250 m height lie at water depths of 600 to 900 m. The cold-water coral reef ecosystems associated with these structures are considered to be “hotspots” of organic carbon mineralization and microbial systems. To establish a depositional and biogeochemical/diagenetic model for cold-water carbonate mounds, Challenger Mound and adjacent continental slope sites were drilled in May 2005 during IODP Expedition 307. One major objective was to test whether deep sub-surface hydrocarbon flow and enhanced microbial activity within the mound structure was important in producing and stabilizing these sedimentary structures.Drilling results showed that the Challenger mound succession (IODP Site U1317) is 130 to 150 meters thick, and mainly consists of floatstone and rudstone facies formed of fine sediments and cold-water branching corals. Pronounced recurring cycles on the scales of several meters are recognized in carbonate content (up to 70% carbonate) and color reflectance, and are probably associated with Pleistocene glacial-interglacial cycles. A role for methane seepage and subsequent anaerobic oxidation was discounted both as a hard-round substrate for mound initiation and as a principal source of carbonate within the mound succession. A broad sulfate-methane transition (approximately 50 m thick) within the Miocene sediments suggested that the zone of anaerobic oxidation of methane principally occurs below the moundbase. In the mound sediments, interstitial water profiles of sulfate, alkalinity, Mg, and Sr suggested a tight coupling between carbonate diagenesis and low rates of microbial sulfate reduction. Overall organic carbon mineralization within cold-water coral mound appeared to be dominated by low rates of iron- and sulfate-reduction that occur in discrete layers within the mound. This was consistent with distributions of total cell-counts, acetate turnover (Webster et al. 2009) and hydrogenase activity (Soffiento et al. 2009). However, biomarker lipid distributions suggested that the Miocene sediments underlying the mound, into which sulfate is diffusing, as well as the sediments from the non-cold water coral reference site (U1318) contain higher abundances of living microbes. The results obtained from Expedition 307 are consistent with a picture emerging from other biogeochemical studies of cold-water coral mound and reef sites. Unless impacted by some external forcing (e.g. fluid flow or erosion event), the microbial activity in the underlying cold-water coral mound sediments is largely decoupled from the highly diverse, active surface ecosystem
Hinode Calibration for Precise Image Co-alignment between SOT and XRT (November 2006 -- April 2007)
To understand the physical mechanisms for activity and heating in the solar
atmosphere, the magnetic coupling from the photosphere to the corona is an
important piece of information from the Hinode observations, and therefore
precise positional alignment is required among the data acquired by different
telescopes. The Hinode spacecraft and its onboard telescopes were developed to
allow us to investigate magnetic coupling with co-alignment accuracy better
than 1 arcsec. Using the Mercury transit observed on 8 November 2006 and
co-alignment measurements regularly performed on a weekly basis, we have
determined the information necessary for precise image co-alignment and have
confirmed that co-alignment better than 1 arcsec can be realized between Solar
Optical Telescope (SOT) and X-Ray Telescope (XRT) with our baseline
co-alignment method. This paper presents results from the calibration for
precise co-alignment of CCD images from SOT and XRT.Comment: 8 pages, 9 figures, accepted for publication in PASJ (Hinode Special
issue
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