188,015 research outputs found

### Can cold quark matter be solid?

The state of cold quark matter really challenges both astrophysicists and
particle physicists, even many-body physicists. It is conventionally suggested
that BCS-like color superconductivity occurs in cold quark matter; however,
other scenarios with a ground state rather than of Fermi gas could still be
possible. It is addressed that quarks are dressed and clustering in cold quark
matter at realistic baryon densities of compact stars, since a weakly coupling
treatment of the interaction between constituent quarks would not be reliable.
Cold quark matter is conjectured to be in a solid state if thermal kinematic
energy is much lower than the interaction energy of quark clusters, and such a
state could be relevant to different manifestations of pulsar-like compact
stars.Comment: Proceedings of IWARA2009 (IJMP D

### Solid Quark Stars?

It is conjectured that cold quark matter with much high baryon density could
be in a solid state, and strange stars with low temperatures should thus be
solid stars. The speculation could be close to the truth if no peculiar
polarization of thermal X-ray emission (in, e.g., RXJ1856), or no gravitational
wave in post-glitch phases, is detected in future advanced facilities, or if
spin frequencies beyond the critical ones limited by r-mode instability are
discovered. The shear modulus of solid quark matter could be ~ 10^{32} erg/cm^3
if the kHz QPOs observed are relevant to the eigenvalues of the center star
oscillations.Comment: Revised significantly, ApJL accepted, or at
http://vega.bac.pku.edu.cn/~rxxu/publications/index_P.ht

### Instability development of a viscous liquid drop impacting a smooth substrate

We study the instability development during a viscous liquid drop impacting a
smooth substrate, using high speed photography. The onset time of the
instability highly depends on the surrounding air pressure and the liquid
viscosity: it decreases with air pressure with the power of minus two, and
increases linearly with the liquid viscosity. From the real-time dynamics
measurements, we construct a model which compares the destabilizing stress from
air with the stabilizing stress from liquid viscosity. Under this model, our
experimental results indicate that at the instability onset time, the two
stresses balance each other. This model also illustrates the different
mechanisms for the inviscid and viscous regimes previously observed: the
inviscid regime is stabilized by the surface tension and the viscous regime is
stabilized by the liquid viscosity.Comment: 4 pages, 5 figure

### On the rigidity theorems for Lagrangian translating solitons in pseudo-Euclidean space II

Let $u$ be a smooth convex function in $\mathbb{R}^{n}$ and the graph
$M_{\nabla u}$ of $\nabla u$ be a space-like translating soliton in
pseudo-Euclidean space $\mathbb{R}^{2n}_{n}$ with a translating vector
$\frac{1}{n}(a_{1}, a_{2}, \cdots, a_{n}; b_{1}, b_{2}, \cdots, b_{n})$, then
the function $u$ satisfies $\det D^{2}u=\exp \left\{ \sum_{i=1}^n-
a_i\frac{\partial u}{\partial x_{i}} +\sum_{i=1}^n b_ix_i+c\right\} \qquad
\hbox{on}\qquad\mathbb R^n$ where $a_i$, $b_i$ and $c$ are constants. The
Bernstein type results are obtained in the course of the arguments.Comment: 9 page

### Observations of Cygnus X-1 in the MeV band by the INTEGRAL imager

The spectrum of the MeV tail detected in the black-hole candidate Cygnus X-1
remains controversial as it appeared much harder when observed with the
INTEGRAL Imager IBIS than with the INTEGRAL spectrometer SPI or CGRO. We
present an independent analysis of the spectra of Cygnus X-1 observed by IBIS
in the hard and soft states. We developed a new analysis software for the
PICsIT detector layer and for the Compton mode data of the IBIS instrument and
calibrated the idiosyncrasies of the PICsIT front-end electronics. The spectra
of Cygnus X-1 obtained for the hard and soft states with the INTEGRAL imager
IBIS are compatible with those obtained with the INTEGRAL spectrometer SPI,
with CGRO, and with the models that attribute the MeV hard tail either to
hybrid thermal/non-thermal Comptonisation or to synchrotron emission.Comment: 6 pages, 7 figure

### Can the age discrepancies of neutron stars be circumvented by an accretion-assisted torque?

It is found that 1E 1207.4-5209 could be a low-mass bare strange star if its
small radius or low altitude cyclotron formation can be identified. The age
problems of five sources could be solved by a fossil-disk-assisted torque. The
magnetic dipole radiation dominates the evolution of PSR B1757-24 at present,
and the others are in propeller (or tracking) phases.Comment: ApJL accepted, or at
http://vega.bac.pku.edu.cn/~rxxu/publications/index_P.ht

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