1,292 research outputs found
Transmission and Reflection of Collective Modes in Spin-1 Bose-Einstein Condensate
We study tunneling properties of collective excitations in spin-1
Bose-Einstein condensates. In the absence of magnetic fields, the total
transmission in the long wavelength limit occurs in all kinds of excitations
but the quadrupolar spin mode in the ferromagnetic state. The quadrupolar spin
mode alone shows the total reflection. A difference between those excitations
comes from whether the wavefunction of an excitation corresponds to that of the
condensate in the long wavelength limit. The correspondence results in the
total transmission as in the spinless BEC.Comment: 6 pages, 5 figure
Estimation of Organ Biodistribution of Activities in Human from External Measurement with TLD
開始ページ、終了ページ: 冊子体のページ付
Towards first-principles understanding of the metal-insulator transition in fluid alkali metals
By treating the electron-ion interaction as perturbation in the
first-principles Hamiltonian, we have calculated the density response functions
of a fluid alkali metal to find an interesting charge instability due to
anomalous electronic density fluctuations occurring at some finite wave vector
{\bi Q} in a dilute fluid phase above the liquid-gas critical point. Since
|{\bi Q}| is smaller than the diameter of the Fermi surface, this instability
necessarily impedes the electric conduction, implying its close relevance to
the metal-insulator transition in fluid alkali metals.Comment: 11 pages, 5 figure
A Search for Near-Infrared Emission From the Halo of NGC 5907 at Radii of 10 kpc to 30 kpc
We present a search for near-infrared (3.5-5 micron) emission from baryonic
dark matter in the form of low-mass stars and/or brown dwarfs in the halo of
the nearby edge-on spiral galaxy NGC 5907. The observations were made using a
256 by 256 InSb array with a pixel scale of 17" at the focus of a
liquid-helium-cooled telescope carried above the Earth's atmosphere by a
sounding rocket. In contrast to previous experiments which have detected a halo
around NGC 5907 in the V, R, I, J and K bands at galactic radii 6kpc < r <
10kpc, our search finds no evidence for emission from a halo at 10kpc < r <
30kpc. Assuming a halo mass density scaling as r^(-2), which is consistent with
the flat rotation curves that are observed out to radii of 32kpc, the lower
limit of the mass-to-light ratio at 3.5-5 microns for the halo of NGC 5907 is
250 (2 sigma) in solar units. This is comparable to the lower limit we have
found previously for NGC 4565 (Uemizu et al. 1998). Based on recent models, our
non-detection implies that hydrogen- burning stars contribute < 15% of the mass
of the dark halo of NGC 5907. Our results are consistent with the previous
detection of extended emission at r < 10kpc if the latter is caused by a
stellar population that has been ejected from the disk because of tidal
interactions. We conclude that the dark halo of NGC 5907, which is evident from
rotation curves that extend far beyond 10kpc, is not comprised of hydrogen
burning stars.Comment: 12 pages, LateX, plus 6 ps figures. Accepted by ApJ. minor changes,
added references, corrected typo
The Nambu-Jona-Lasinio Chiral Soliton with Constrained Baryon Number
A regularization for the baryon number consistent with the energy in the
Nambu-Jona-Lasinio model is introduced. The soliton solution is constructed
with the regularized baryon number constrained to unity. It is furthermore
demonstrated that this constraint prevents the soliton from collapsing when
scalar fields are allowed to be space dependent. In this scheme the scalar
fields actually vanish at the origin reflecting a partial restoration of chiral
symmetry. Also the influence of this constraint on some static properties of
baryons is discussed.Comment: 10 LaTeX pages 4 figures, report no UNITU-THEP-7/199
TGLI1 transcription factor mediates breast cancer brain metastasis via activating metastasis-initiating cancer stem cells and astrocytes in the tumor microenvironment
Mechanisms for breast cancer metastasis remain unclear. Whether truncated glioma-associated oncogene homolog 1 (TGLI1), a transcription factor known to promote angiogenesis, migration and invasion, plays any role in metastasis of any tumor type has never been investigated. In this study, results of two mouse models of breast cancer metastasis showed that ectopic expression of TGLI1, but not GLI1, promoted preferential metastasis to the brain. Conversely, selective TGLI1 knockdown using antisense oligonucleotides led to decreased breast cancer brain metastasis (BCBM) in vivo. Immunohistochemical staining showed that TGLI1, but not GLI1, was increased in lymph node metastases compared to matched primary tumors, and that TGLI1 was expressed at higher levels in BCBM specimens compared to primary tumors. TGLI1 activation is associated with a shortened time to develop BCBM and enriched in HER2-enriched and triple-negative breast cancers. Radioresistant BCBM cell lines and specimens expressed higher levels of TGLI1, but not GLI1, than radiosensitive counterparts. Since cancer stem cells (CSCs) are radioresistant and metastasis-initiating cells, we examined TGLI1 for its involvement in breast CSCs and found TGLI1 to transcriptionally activate stemness genes CD44, Nanog, Sox2, and OCT4 leading to CSC renewal, and TGLI1 outcompetes with GLI1 for binding to target promoters. We next examined whether astrocyte-priming underlies TGLI1-mediated brain tropism and found that TGLI1-positive CSCs strongly activated and interacted with astrocytes in vitro and in vivo. These findings demonstrate, for the first time, that TGLI1 mediates breast cancer metastasis to the brain, in part, through promoting metastasis-initiating CSCs and activating astrocytes in BCBM microenvironment
Absence of Anomalous Tunneling of Bogoliubov Excitations for Arbitrary Potential Barrier under the Critical Condensate Current
We derive the exact solution of low energy limit of Bogoliubov equations for
excitations of Bose-Einstein condensate in the presence of arbitrary potential
barrier and maximum current of condensate. Using this solution, we give the
explicit expression for the transmission coefficient against the potential
barrier, which shows partial transmission in the low energy limit. The
wavefunctions of excitations in the low energy limit do not coincide with that
of the condensate. The absence of the perfect transmission in the critical
current state originates from local enhancement of density fluctuations around
the potential barrier.Comment: 4 pages, 1 figur
Limit distributions of two-dimensional quantum walks
One-parameter family of discrete-time quantum-walk models on the square
lattice, which includes the Grover-walk model as a special case, is
analytically studied. Convergence in the long-time limit of all
joint moments of two components of walker's pseudovelocity, and
, is proved and the probability density of limit distribution is
derived. Dependence of the two-dimensional limit density function on the
parameter of quantum coin and initial four-component qudit of quantum walker is
determined. Symmetry of limit distribution on a plane and localization around
the origin are completely controlled. Comparison with numerical results of
direct computer-simulations is also shown.Comment: v3: REVTeX4, 20 pages, 6 figures, minor corrections made for
publicatio
Global monopole solutions in Horava gravity
In Horava's theory of gravity coupled to a global monopole source, we seek
for static, spherically symmetric spacetime solutions for general values of
. We obtain the explicit solutions with deficit solid angles, in the
IR modified Horava gravity model, at the IR fixed point and at the
conformal point . For the other values of we also
find special solutions to the inhomogenous equation of the gravity model with
detailed balance, and we discuss an possibility of astrophysical applications
of the solution that has a deficit angle for a finite range.Comment: 7 pages, added reference
Robust Time Estimation Reconciles Views of the Antiquity of Placental Mammals
BACKGROUND: Molecular studies have reported divergence times of modern placental orders long before the Cretaceous–Tertiary boundary and far older than paleontological data. However, this discrepancy may not be real, but rather appear because of the violation of implicit assumptions in the estimation procedures, such as non-gradual change of evolutionary rate and failure to correct for convergent evolution. METHODOLOGY/PRINCIPAL FINDINGS: New procedures for divergence-time estimation robust to abrupt changes in the rate of molecular evolution are described. We used a variant of the multidimensional vector space (MVS) procedure to take account of possible convergent evolution. Numerical simulations of abrupt rate change and convergent evolution showed good performance of the new procedures in contrast to current methods. Application to complete mitochondrial genomes identified marked rate accelerations and decelerations, which are not obtained with current methods. The root of placental mammals is estimated to be ∼18 million years more recent than when assuming a log Brownian motion model. Correcting the pairwise distances for convergent evolution using MVS lowers the age of the root about another 20 million years compared to using standard maximum likelihood tree branch lengths. These two procedures combined revise the root time of placental mammals from around 122 million years ago to close to 84 million years ago. As a result, the estimated distribution of molecular divergence times is broadly consistent with quantitative analysis of the North American fossil record and traditional morphological views. CONCLUSIONS/SIGNIFICANCE: By including the dual effects of abrupt rate change and directly accounting for convergent evolution at the molecular level, these estimates provide congruence between the molecular results, paleontological analyses and morphological expectations. The programs developed here are provided along with sample data that reproduce the results of this study and are especially applicable studies using genome-scale sequence lengths
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