310 research outputs found
Vacuum entanglement governs the bosonic character of magnons
It is well known that magnons, elementary excitations in a magnetic material,
behave as bosons when their density is low. We study how the bosonic character
of magnons is governed by the amount of a multipartite entanglement in the
vacuum state on which magnons are excited. We show that if the multipartite
entanglement is strong, magnons cease to be bosons. We also consider some
examples, such as ground states of the Heisenberg ferromagnet and the
transverse Ising model, the condensation of magnons, the one-way quantum
computer, and Kitaev's toric code. Our result provides insights into the
quantum statistics of elementary excitations in these models, and into the
reason why a non-local transformation, such as the Jordan-Wigner
transformation, is necessary for some many-body systems.Comment: 4 pages, no figur
A Fast Algorithm for Solving the Poisson Equation on a Nested Grid
We present a numerical method for solving the Poisson equation on a nested
grid. The nested grid consists of uniform grids having different grid spacing
and is designed to cover the space closer to the center with a finer grid. Thus
our numerical method is suitable for computing the gravity of a centrally
condensed object. It consists of two parts: the difference scheme for the
Poisson equation on the nested grid and the multi-grid iteration algorithm. It
has three advantages: accuracy, fast convergence, and scalability. First it
computes the gravitational potential of a close binary accurately up to the
quadraple moment, even when the binary is resolved only in the fine grids.
Second residual decreases by a factor of 300 or more by each iteration. We
confirmed experimentally that the iteration converges always to the exact
solution of the difference equation. Third the computation load of the
iteration is proportional to the total number of the cells in the nested grid.
Thus our method gives a good solution at the minimum expense when the nested
grid is large. The difference scheme is applicable also to the adaptive mesh
refinement in which cells of different sizes are used to cover a domain of
computation.Comment: 22 pages 21 figures. To appear in Ap
Fragmentation of a Molecular Cloud Core versus Fragmentation of the Massive Protoplanetary Disk in the Main Accretion Phase
The fragmentation of molecular cloud cores a factor of 1.1 denser than the
critical Bonnor-Ebert sphere is examined though three-dimensional numerical
simulations. A nested grid is employed to resolve fine structure down to 1 AU
while following the entire structure of the molecular cloud core of radius 0.14
pc. A total of 225 models are shown to survey the effects of initial rotation
speed, rotation law, and amplitude of bar mode perturbation. The simulations
show that the cloud fragments whenever the cloud rotates sufficiently slowly to
allow collapse but fast enough to form a disk before first-core formation. The
latter condition is equivalent to , where
and denote the initial central angular velocity and the
freefall time measured from the central density, respectively. Fragmentation is
classified into six types: disk-bar, ring-bar, satellite, bar, ring, and
dumbbell types according to the morphology of collapse and fragmentation. When
the outward decrease in initial angular velocity is more steep, the cloud
deforms from spherical at an early stage. The cloud deforms into a ring only
when the bar mode m = 2 perturbation is very minor. The ring fragments into two
or three fragments via ring-bar type fragmentation and into at least three
fragments via ring type fragmentation. When the bar mode is significant, the
cloud fragments into two fragments via either bar or dumbbell type
fragmentation. These fragments eventually merge due to their low angular
momenta, after which several new fragments form around the merged fragment via
satellite type fragmentation.Comment: Accepted by ApJ, 53 pages, 27 figures. Document with high quality
figures and movies are available in
http://meric.i.hosei.ac.jp/~matsu/fragment03
Delta degrees of freedom in antisymmetrized molecular dynamics and (p,p') reactions in the delta region
Delta degrees of freedom are introduced into antisymmetrized molecular
dynamics (AMD). This is done by increasing the number of basic states in the
AMD wave function, introducing a Skyrme-type delta-nucleon potential, and
including reactions in the collision description.
As a test of the delta dynamics, the extended AMD is applied to (p,p)
recations at MeV for a C target. It is found that the
ratio and the absolute values for delta peak and quasielastic peak (QEP) in the
C(p,p) reaction are reproduced for angles \Theta_{\rm lab} \agt
40^\circ, pointing to a correct treatment of the delta dynamics in the
extended AMD. For forward angles the QEP is overestimated. The results of the
AMD calculations are compared to one-step Monte Carlo (OSMC) calculations and a
detailed analysis of multi-step and delta potential effects is given. As
important side results we present a way to apply a Gallilei invariant theory
for (N,N) reactions up to MeV which ensures
approximate Lorentz invariance and we discuss how to fix the width parameter
of the single particle momentum distribution for outgoing nucleons in the
AMD calculation.Comment: 28 pages, revtex, 12 figures included, figures are also available
upon request as postscript files from the authors (e-mail:
[email protected]), submitted to Phys. Rev.
Proton inelastic scattering to continuum studied with antisymmetrized molecular dynamics
Intermediate energy (p,px) reaction is studied with antisymmetrized
molecular dynamics (AMD) in the cases of Ni target with MeV
and C target with 200 and 90 MeV. Angular distributions for
various energies are shown to be reproduced well without any
adjustable parameter, which shows the reliability and usefulness of AMD in
describing light-ion reactions. Detailed analyses of the calculations are made
in the case of Ni target and following results are obtained: Two-step
contributions are found to be dominant in some large angle region and to be
indispensable for the reproduction of data. Furthermore the reproduction of
data in the large angle region \theta \agt 120^\circ for = 100 MeV
is shown to be due to three-step contributions. Angular distributions for
E_{p'} \agt 40 MeV are found to be insensitive to the choice of different
in-medium nucleon-nucleon cross sections and the reason of this
insensitivity is discussed in detail. On the other hand, the total reaction
cross section and the cross section of evaporated protons are found to be
sensitive to . In the course of the analyses of the calculations,
comparison is made with the distorted wave approach.Comment: 16 pages, 7 Postscript figure
Computational Indistinguishability between Quantum States and Its Cryptographic Application
We introduce a computational problem of distinguishing between two specific
quantum states as a new cryptographic problem to design a quantum cryptographic
scheme that is "secure" against any polynomial-time quantum adversary. Our
problem, QSCDff, is to distinguish between two types of random coset states
with a hidden permutation over the symmetric group of finite degree. This
naturally generalizes the commonly-used distinction problem between two
probability distributions in computational cryptography. As our major
contribution, we show that QSCDff has three properties of cryptographic
interest: (i) QSCDff has a trapdoor; (ii) the average-case hardness of QSCDff
coincides with its worst-case hardness; and (iii) QSCDff is computationally at
least as hard as the graph automorphism problem in the worst case. These
cryptographic properties enable us to construct a quantum public-key
cryptosystem, which is likely to withstand any chosen plaintext attack of a
polynomial-time quantum adversary. We further discuss a generalization of
QSCDff, called QSCDcyc, and introduce a multi-bit encryption scheme that relies
on similar cryptographic properties of QSCDcyc.Comment: 24 pages, 2 figures. We improved presentation, and added more detail
proofs and follow-up of recent wor
High-Resolution Near-Infrared Polarimetry of a Circumstellar Disk around UX Tau A
We present H-band polarimetric imagery of UX Tau A taken with HiCIAO/AO188 on
the Subaru Telescope. UX Tau A has been classified as a pre-transitional disk
object, with a gap structure separating its inner and outer disks. Our imagery
taken with the 0.15 (21 AU) radius coronagraphic mask has revealed a strongly
polarized circumstellar disk surrounding UX Tau A which extends to 120 AU, at a
spatial resolution of 0.1 (14 AU). It is inclined by 46 \pm 2 degree as the
west side is nearest. Although SED modeling and sub-millimeter imagery
suggested the presence of a gap in the disk, with the inner edge of the outer
disk estimated to be located at 25 - 30 AU, we detect no evidence of a gap at
the limit of our inner working angle (23 AU) at the near-infrared wavelength.
We attribute the observed strong polarization (up to 66 %) to light scattering
by dust grains in the disk. However, neither polarization models of the
circumstellar disk based on Rayleigh scattering nor Mie scattering
approximations were consistent with the observed azimuthal profile of the
polarization degrees of the disk. Instead, a geometric optics model of the disk
with nonspherical grains with the radii of 30 micron meter is consistent with
the observed profile. We suggest that the dust grains have experienced frequent
collisional coagulations and have grown in the circumstellar disk of UX Tau A.Comment: 20 pages, 8 figures, and 1 table. accepted to PAS
The Structure of Pre-transitional Protoplanetary Disks I: Radiative Transfer Modeling of the Disk+Cavity in the PDS 70 system
Through detailed radiative transfer modeling, we present a disk+cavity model
to simultaneously explain both the SED and Subaru H-band polarized light
imaging for the pre-transitional protoplanetary disk PDS 70. Particularly, we
are able to match not only the radial dependence, but also the absolute scale,
of the surface brightness of the scattered light. Our disk model has a cavity
65 AU in radius, which is heavily depleted of sub-micron-sized dust grains, and
a small residual inner disk which produces a weak but still optically thick NIR
excess in the SED. To explain the contrast of the cavity edge in the Subaru
image, a factor of ~1000 depletion for the sub-micron-sized dust inside the
cavity is required. The total dust mass of the disk may be on the order of 1e-4
M_sun, only weakly constrained due to the lack of long wavelength observations
and the uncertainties in the dust model. The scale height of the
sub-micron-sized dust is ~6 AU at the cavity edge, and the cavity wall is
optically thick in the vertical direction at H-band. PDS 70 is not a member of
the class of (pre-)transitional disks identified by Dong et al. (2012), whose
members only show evidence of the cavity in the millimeter-sized dust but not
the sub-micron-sized dust in resolved images. The two classes of
(pre-)transitional disks may form through different mechanisms, or they may
just be at different evolution stages in the disk clearing process.Comment: 28 pages (single column), 7 figures, 1 table, ApJ accepte
Targeted Therapy Resistance Mediated by Dynamic Regulation of Extrachromosomal Mutant EGFR DNA
Intratumoral heterogeneity contributes to cancer drug resistance, but the underlying mechanisms are not understood. Single-cell analyses of patient-derived models and clinical samples from glioblastoma patients treated with epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs) demonstrate that tumor cells reversibly up-regulate or suppress mutant EGFR expression, conferring distinct cellular phenotypes to reach an optimal equilibrium for growth. Resistance to EGFR TKIs is shown to occur by elimination of mutant EGFR from extrachromosomal DNA. After drug withdrawal, reemergence of clonal EGFR mutations on extrachromosomal DNA follows. These results indicate a highly specific, dynamic, and adaptive route by which cancers can evade therapies that target oncogenes maintained on extrachromosomal DNA
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