1,036 research outputs found
Rotationally-Driven Fragmentation for the Formation of the Binary Protostellar System L1551 IRS 5
Either bulk rotation or local turbulence is widely invoked to drive
fragmentation in collapsing cores so as to produce multiple star systems. Even
when the two mechanisms predict different manners in which the stellar spins
and orbits are aligned, subsequent internal or external interactions can drive
multiple systems towards or away from alignment thus masking their formation
process. Here, we demonstrate that the geometrical and dynamical relationship
between the binary system and its surrounding bulk envelope provide the crucial
distinction between fragmentation models. We find that the circumstellar disks
of the binary protostellar system L1551 IRS 5 are closely parallel not just
with each other but also with their surrounding flattened envelope.
Measurements of the relative proper motion of the binary components spanning
nearly 30 yr indicate an orbital motion in the same sense as the envelope
rotation. Eliminating orbital solutions whereby the circumstellar disks would
be tidally truncated to sizes smaller than are observed, the remaining
solutions favor a circular or low-eccentricity orbit tilted by up to
25 from the circumstellar disks. Turbulence-driven fragmentation
can generate local angular momentum to produce a coplanar binary system, but
which bears no particular relationship with its surrounding envelope. Instead,
the observed properties conform with predictions for rotationally-driven
fragmentation. If the fragments were produced at different heights or on
opposite sides of the midplane in the flattened central region of a rotating
core, the resulting protostars would then exhibit circumstellar disks parallel
with the surrounding envelope but tilted from the orbital plane as is observed.Comment: Accepted for publication in Ap
Detection of Macroscopic Entanglement by Correlation of Local Observables
We propose a correlation of local observables on many sites in macroscopic
quantum systems. By measuring the correlation one can detect, if any,
superposition of macroscopically distinct states, which we call macroscopic
entanglement, in arbitrary quantum states that are (effectively) homogeneous.
Using this property, we also propose an index of macroscopic entanglement.Comment: Although the index q was proposed for mixed states, it is also
applicable to pure states, on which we fix minor bugs (that will be reported
in PRL as erratum). The conclusions of the paper remain unchanged. (4 pages,
no figures.
The negative Bogoliubov dispersion in exciton-polariton condensates
Bogoliubov's theory states that self-interaction effects in Bose-Einstein
condensates produce a characteristic linear dispersion at low momenta. One of
the curious features of Bogoliubov's theory is that the new quasiparticles in
the system are linear combinations of creation and destruction operators of the
bosons. In exciton-polariton condensates, this gives the possibility of
directly observing the negative branch of the Bogoliubov dispersion in the
photoluminescence (PL) emission. Here we theoretically examine the PL spectra
of exciton-polariton condensates taking into account of reservoir effects. At
sufficiently high excitation densities, the negative dispersion becomes
visible. We also discuss the possibility for relaxation oscillations to occur
under conditions of strong reservoir coupling. This is found to give a
secondary mechanism for making the negative branch visible
Macroscopic entanglement of many-magnon states
We study macroscopic entanglement of various pure states of a one-dimensional
N-spin system with N>>1. Here, a quantum state is said to be macroscopically
entangled if it is a superposition of macroscopically distinct states. To judge
whether such superposition is hidden in a general state, we use an essentially
unique index p: A pure state is macroscopically entangled if p=2, whereas it
may be entangled but not macroscopically if p<2. This index is directly related
to the stability of the state. We calculate the index p for various states in
which magnons are excited with various densities and wavenumbers. We find
macroscopically entangled states (p=2) as well as states with p=1. The former
states are unstable in the sense that they are unstable against some local
measurements. On the other hand, the latter states are stable in the senses
that they are stable against local measurements and that their decoherence
rates never exceed O(N) in any weak classical noises. For comparison, we also
calculate the von Neumann entropy S(N) of a subsystem composed of N/2 spins as
a measure of bipartite entanglement. We find that S(N) of some states with p=1
is of the same order of magnitude as the maximum value N/2. On the other hand,
S(N) of the macroscopically entangled states with p=2 is as small as O(log N)<<
N/2. Therefore, larger S(N) does not mean more instability. We also point out
that these results are analogous to those for interacting many bosons.
Furthermore, the origin of the huge entanglement, as measured either by p or
S(N), is discussed to be due to the spatial propagation of magnons.Comment: 30 pages, 5 figures. The manuscript has been shortened and typos have
been fixed. Data points of figures have been made larger in order to make
them clearly visibl
Study of fast electron generation using multi beam of LFEX-class laser
Fast Ignition Realization Experiment project phase-I (FIREX-I) is being performed at Institute of Laser Engineering, Osaka University. In this project, the four-beam bundled high-energy Petawatt laser (LFEX) is being operated. LFEX laser provides great multi-beam irradiation flexibility, with the possibility of arrange the pulses in temporal sequence, spatially separate them in distinct spots of focus them in a single spot. In this paper, we study the two-beam interference effects on high-intensity picosecond laser-plasma interaction (LPI) by two-dimensional relativistic Particle-In-Cell simulations. The interference causes surface perturbation, which enhances laser absorption and underdense plasma generation, increasing the accelerated electron number and their slope temperature. The laser-to-electron energy conversion efficiency for two-beam interference case is suitable for Fast Ignition (FI) compared to the single beam case, but the increment of fast electron divergence leads to lower energy coupling. To optimize the target design for FI, these interference effects should be taken into consideration
PCRPi, Presaging Critical Residues in Protein interfaces, a new computational tool to chart hot spots in protein interfaces
Proteināprotein interactions (PPIs) are ubiquitous in Biology, and thus offer an enormous potential for the discovery of novel therapeutics. Although protein interfaces are large and lack defining physiochemical traits, is well established that only a small portion of interface residues, the so-called hot spot residues, contribute the most to the binding energy of the protein complex. Moreover, recent successes in development of novel drugs aimed at disrupting PPIs rely on targeting such residues. Experimental methods for describing critical residues are lengthy and costly; therefore, there is a need for computational tools that can complement experimental efforts. Here, we describe a new computational approach to predict hot spot residues in protein interfaces. The method, called Presaging Critical Residues in Protein interfaces (PCRPi), depends on the integration of diverse metrics into a unique probabilistic measure by using Bayesian Networks. We have benchmarked our method using a large set of experimentally verified hot spot residues and on a blind prediction on the protein complex formed by HRAS protein and a single domain antibody. Under both scenarios, PCRPi delivered consistent and accurate predictions. Finally, PCRPi is able to handle cases where some of the input data is either missing or not reliable (e.g. evolutionary information)
Confirmation of a one-dimensional spin-1/2 Heisenberg system with ferromagnetic first-nearest-neighbor and antiferromagnetic second-nearest-neighbor interactions in RbCuMoO
We have investigated magnetic properties of RbCuMoO
powder. Temperature dependence of magnetic susceptibility and magnetic-field
dependence of magnetization have shown that this cuprate is a model compound of
a one-dimensional spin-1/2 Heisenberg system with ferromagnetic
first-nearest-neighbor (1NN) and antiferromagnetic second-nearest-neighbor
(2NN) competing interactions (competing system). Values of the 1NN and 2NN
interactions are estimated as K and K (). This value of suggests that the ground state is a
spin-singlet incommensurate state. In spite of relatively large and
, no magnetic phase transition appears down to 2 K, while an
antiferromagnetic transition occurs in other model compounds of the competing
system with ferromagnetic 1NN interaction. For that reason,
RbCuMoO is an ideal model compound to study properties of
the incommensurate ground state that are unconfirmed experimentally.Comment: 6 pages, 4 figure
Algebraic entropy and the space of initial values for discrete dynamical systems
A method to calculate the algebraic entropy of a mapping which can be lifted
to an isomorphism of a suitable rational surfaces (the space of initial values)
are presented. It is shown that the degree of the th iterate of such a
mapping is given by its action on the Picard group of the space of initial
values. It is also shown that the degree of the th iterate of every
Painlev\'e equation in sakai's list is at most and therefore its
algebraic entropy is zero.Comment: 10 pages, pLatex fil
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
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