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49 - A. Chen , A. Wang , C. Broadbent 2014
Accurate measurement of the fat-to-muscle ratio in animal model is important for obesity research. An efficient way to measure the fat to muscle ratio in animal model using dual-energy absorptiometry is presented in this paper. A radioactive source e xciting x-ray fluorescence from a target material is used to provide the two x-ray energies needed. The x-rays, after transmitting through the sample, are measured with an energy-sensitive Ge detector. Phantoms and specimens were measured. The results showed that the method was sensitive to the fat to muscle ratios with good linearity. A standard deviation of a few percent in the fat to muscle ratio could be observed with the x-ray dose of 0.001 mGy.
305 - Jungkai A. Chen , Zhi Jiang 2013
We continue our study on smooth complex projective varieties $X$ of maximal Albanese dimension and of general type satisfying $chi(X, omega_X)=0$. We formulate a conjectural characterization of such varieties and prove this conjecture when the Albanese variety has only three simple factors.
364 - Jungkai A. Chen , Meng Chen 2013
We prove the Conjecture of Catenese--Chen--Zhang: the inequality $K_X^3geq frac{4}{3}p_g(X)-frac{10}{3}$ holds for all projective Gorenstein minimal 3-folds $X$ of general type.
225 - Jungkai A. Chen , Meng Chen 2013
Nonsingular projective 3-folds $V$ of general type can be naturally classified into 18 families according to the {it pluricanonical section index} $delta(V):=text{min}{m|P_mgeq 2}$ since $1leq delta(V)leq 18$ due to our previous series (I, II). Based on our further classification to 3-folds with $delta(V)geq 13$ and an intensive geometrical investigation to those with $delta(V)leq 12$, we prove that $text{Vol}(V) geq frac{1}{1680}$ and that the pluricanonical map $Phi_{m}$ is birational for all $m geq 61$, which greatly improves known results. An optimal birationality of $Phi_m$ for the case $delta(V)=2$ is obtained. As an effective application, we study projective 4-folds of general type with $p_ggeq 2$ in the last section.
495 - A. Shemyakin , C. Baffes , A. Chen 2013
The Project X Injector Experiment (PXIE), a test bed for the Project X front end, will be completed at Fermilab at FY12-16. One of the challenging goals of PXIE is demonstration of the capability to form a 1 mA H- beam with an arbitrary selected bunc h pattern from the initially 5 mA 162.5 MHz CW train. The bunch selection will be made in the Medium Energy Beam Transport (MEBT) at 2.1 MeV by diverting undesired bunches to an absorber. This paper presents the MEBT scheme and describes development of its elements, including the kickers and absorber.
The uncertainty in the 29P(p,gamma)30S reaction rate over the temperature range of 0.1 - 1.3 GK was previously determined to span ~4 orders of magnitude due to the uncertain location of two previously unobserved 3+ and 2+ resonances in the 4.7 - 4.8 MeV excitation region in 30S. Therefore, the abundances of silicon isotopes synthesized in novae, which are relevant for the identification of presolar grains of putative nova origin, were uncertain by a factor of 3. To investigate the level structure of 30S above the proton threshold (4394.9(7) keV), a charged-particle spectroscopy and an in-beam gamma-ray spectroscopy experiments were performed. Differential cross sections of the 32S(p,t)30S reaction were measured at 34.5 MeV. Distorted wave Born approximation calculations were performed to constrain the spin-parity assignments of the observed levels. An energy level scheme was deduced from gamma-gamma coincidence measurements using the 28Si(3He,n-gamma)30S reaction. Spin-parity assignments based on measurements of gamma-ray angular distributions and gamma-gamma directional correlation from oriented nuclei were made for most of the observed levels of 30S. As a result, the resonance energies corresponding to the excited states in 4.5 MeV - 6 MeV region, including the two astrophysically important states predicted previously, are measured with significantly better precision than before. The uncertainty in the rate of the 29P(p,gamma)30S reaction is substantially reduced over the temperature range of interest. Finally, the influence of this rate on the abundance ratios of silicon isotopes synthesized in novae are obtained via 1D hydrodynamic nova simulations.
193 - Jungkai A. Chen , Meng Chen 2010
Let $V$ be a complex nonsingular projective 3-fold of general type. We shall give a detailed classification up to baskets of singularities on a minimal model of $V$. We show that the $m$-canonical map of $V$ is birational for all $mgeq 73$ and that t he canonical volume $text{Vol}(V)geq {1/2660}$. When $chi(mathcal{O}_V)leq 1$, our result is $text{Vol}(V)geq {1/420}$, which is optimal. Other effective results are also included in the paper.
248 - Jungkai A. Chen , Meng Chen 2009
Let $V$ be a complex nonsingular projective 3-fold of general type. We prove $P_{12}(V):=text{dim} H^0(V, 12K_V)>0$ and $P_{m_0}(V)>1$ for some positive integer $m_0leq 24$. A direct consequence is the birationality of the pluricanonical map $varphi_ m$ for all $mgeq 126$. Besides, the canonical volume $text{Vol}(V)$ has a universal lower bound $ u(3)geq frac{1}{63cdot 126^2}$.
We show that 3-fold terminal flips and divisorial contractions to a curve may be factored by a sequence of weighted blow-ups, flops, blow-downs to a locally complete intersection curve in a smooth 3-fold or divisorial contractions to a point.
The present work reports the results of 30S radioactive beam development for a future experiment directly measuring data to extrapolate the 30S(alpha,p) stellar reaction rate in Type I X-ray bursts, a phenomena where nuclear explosions occur repeated ly on the surface of accreting neutron stars. We produce the radioactive ion 30S via the 3He(28Si,30S)n reaction, by bombarding a cryogenically cooled target of 3He at 400 Torr and 80 K with 28Si beams of 6.9 and 7.54 MeV/u. In order to perform a successful future experiment which allows us to calculate the stellar 30S(alpha, p) reaction rate, Hauser-Feshbach calculations indicate we require a 30S beam of ~10^5 particles per second at ~32 MeV. Based on our recent beam development experiments in 2006 and 2008, it is believed that such a beam may be fabricated in 2009 according to the results presented. We plan to measure the 4He(30S,p) cross-section at astrophysical energies in 2009, and some brief remarks on the planned (alpha,p) technique are also elucidated.
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