Inward Motions of the Compact SiO Masers Around VX Sagittarii

We report Very Long Baseline Array (VLBA) observations of 43 GHz v=1, J=1-0 SiO masers in the circumstellar envelope of the M-type semi-regular variable star VX Sgr at 3 epochs during 1999 April-May. These high-resolution VLBA images reveal a persistent ringlike distribution of SiO masers with a projected radius of ~3 stellar radii. The typical angular size of 0.5 mas for individual maser feature was estimated from two-point correlation function analysis for maser spots. We found that the apparent size scale of maser features was distinctly smaller than that observed in the previous observations by comparing their fractions of total power imaged. This change in the size scale of maser emission may be related to stellar activity that caused a large SiO flare during our observations. Our observations confirmed the asymmetric distribution of maser emission, but the overall morphology has changed significantly with the majority of masers clustering to the north-east of the star compared to that lying to the south-west direction in 1992. By identifying 42 matched maser features appearing in all the three epochs, we determined the contraction of an SiO maser shell toward VX Sgr at a proper motion of -0.507 mas/yr, corresponding to a velocity of about 4 km/s at a distance of 1.7 kpc to VX Sgr. Such a velocity is on the order of the sound speed, and can be easily explained by the gravitational infall of material from the circumstellar dust shell.Comment: 26 pages, 5 figures, 4 tables, accepted for publication in Ap

Observation of a red-blue detuning asymmetry in matter-wave superradiance

We report the first experimental observations of strong suppression of matter-wave superradiance using blue-detuned pump light and demonstrate a pump-laser detuning asymmetry in the collective atomic recoil motion. In contrast to all previous theoretical frameworks, which predict that the process should be symmetric with respect to the sign of the pump-laser detuning, we find that for condensates the symmetry is broken. With high condensate densities and red-detuned light, the familiar distinctive multi-order, matter-wave scattering pattern is clearly visible, whereas with blue-detuned light superradiance is strongly suppressed. In the limit of a dilute atomic gas, however, symmetry is restored.Comment: Accepted by Phys. Rev. Let

Homeobox gene Rhox5 is regulated by epigenetic mechanisms in cancer and stem cells and promotes cancer growth

<p>Abstract</p> <p>Background</p> <p>Homeobox genes murine <it>Rhox5 </it>and human <it>RHOXF1 </it>are expressed in early embryonic stages and then mostly restricted to germline tissues in normal adult, yet they are aberrantly expressed in cancer cells <it>in vitro </it>and <it>in vivo </it>. Here we study the epigenetic regulation and potential functions of <it>Rhox5 </it>gene.</p> <p>Findings</p> <p>In <it>Rhox5 </it>-silenced or extremely low expresser cells, we observed low levels of active histone epigenetic marks (H3ac, H4ac and H3K4me2) and high levels of repressive mark H3K9me2 along with DNA hypermethylation in the promoter. In <it>Rhox5 </it>low expresser cells, we typically observed modest levels of both active and repressive histone marks along with moderate DNA methylation. In <it>Rhox5 </it>highly expressed CT26 cancer cells, we observed DNA hypomethylation along with high levels of both active and repressive histone marks. Epigenetic drugs (retinoic acid and MS-275) induced F9 cell differentiation with enhanced <it>Rhox5 </it>expression and dynamic changes of epigenetic marks. Finally, <it>Rhox5 </it>knockdown by small hairpin RNA (shRNA) in CT26 colon cancer decreased cell proliferation and migration <it>in vitro </it>and tumor growth <it>in vivo </it>.</p> <p>Conclusions</p> <p>Both DNA methylation and histone methylation/acetylation play key roles in modulating <it>Rhox5 </it>expression in various cell types. The stem cell-like "bivalent domain", an epigenetic feature originally identified in key differentiation genes within stem cells, exists in the <it>Rhox5 </it>gene promoter in not only embryonic stem cells but also cancer cells, cancer stem cells, and differentiated Sertoli cells. As <it>Ras </it>signaling-dependent <it>Rhox5 </it>expression promotes tumor growth, <it>Rhox5 </it>may be an ideal target for therapeutic intervention in cancer.</p

Vector meson photoproduction studied in its radiative decay channel

We provide an analysis of vector meson photoproduction in the channel of the vector meson decaying into a pseudoscalar meson plus a photon, i.e. $V\to P\gamma$. It is shown that non-trivial kinematic correlations arise from the measurement of the $P\gamma$ angular distributions in the overall c.m. system in comparison with those in the vector-meson-rest frame. In terms of the vector meson density matrix elements, the implication of such kinematic correlations in the measurement of polarization observables is discussed. For the $\omega$ meson production, due to its relatively large branching ratios for $\omega\to\pi^0\gamma$, additional events from this channel may enrich the information about the reaction mechanism and improve the statistics of the recent measurement of polarized beam asymmetries by the GRAAL Collaboration. For $\phi\to \eta\gamma$, $\rho\to \pi\gamma$, and $K^*\to K\gamma$, we expect that additional information about the spin structure of the vector meson production vertex can be derived.Comment: Revtex, 14 pages, 2 eps figures; Version accepted by PR

CP violation in the inclusive b -> s g decay in the framework of multi Higgs doublet models

We study the decay width and CP asymmetry of the inclusive process b--> s g (g denotes gluon) in the multi Higgs doublet models with complex Yukawa couplings, including next to leading QCD corrections. We analyse the dependencies of the decay width and CP asymmetry on the scale \mu and CP violating parameter \theta. We observe that there exist an enhancement in the decay width and CP asymmetry is at the order of 10^{-2}.Comment: 11 pages, 8 Figure

First Digit Distribution of Hadron Full Width

A phenomenological law, called Benford's law, states that the occurrence of the first digit, i.e., $1,2,...,9$, of numbers from many real world sources is not uniformly distributed, but instead favors smaller ones according to a logarithmic distribution. We investigate, for the first time, the first digit distribution of the full widths of mesons and baryons in the well defined science domain of particle physics systematically, and find that they agree excellently with the Benford distribution. We also discuss several general properties of Benford's law, i.e., the law is scale-invariant, base-invariant, and power-invariant. This means that the lifetimes of hadrons follow also Benford's law.Comment: 8 latex pages, 4 figures, final version in journal publicatio

Exotic Hadrons Of Minimal Pentaquark (qqqq\Bar{Q}) States

It is shown that the exotic non-qqq hadrons of pentaquark $qqqq\bar{q}$ states can be clearly distinguished from the conventional qqq-baryon resonances or their hybrids if the flavor of $\bar{q}$ is different from any of the other four quarks. We suggest the physical process $p(e,e'K^-)Z(uuud\bar{s})$, which can be investigated at the Thomas Jefferson National Accelerator Facility (JLab), as an ideal process to search for the existence or non-existence of the exotic hadron of minimal pentaquark state $Z(uuud\bar{s})$. (The search for the existence of $Z(uudd\bar{s})$ is also discussed in the paper. We added this sentence after the original published form of this paper.)Comment: 7 latex pages, 1 figur

Spontaneous separation of two-component Fermi gases in a double-well trap

The two-component Fermi gas in a double-well trap is studied using the density functional theory and the density profile of each component is calculated within the Thomas-Fermi approximation. We show that the two components are spatially separate in the two wells once the repulsive interaction exceeds the Stoner point, signaling the occurrence of the ferromagnetic transition. Therefore, the double-well trap helps to explore itinerant ferromagnetism in atomic Fermi gases, since the spontaneous separation can be examined by measuring component populations in one well.Comment: 6 pages, 6 figures, to appear in ep