Hasil untuk "astro-ph"

D. Santos, T. Goto, T. Lu et al.

As recent advancements in physics and astronomy rapidly rewrite textbooks, there is a growing need in keeping abreast of the latest knowledge in these fields. Reading preprints is one of the effective ways to do this. By having journal clubs where people can read and discuss journals together, the benefits of reading journals become more prevalent. We present an investigative study of understanding the factors that affect the success of preprint journal clubs in astronomy, more commonly known as Astro-ph/Astro-Coffee (hereafter called AC). A survey was disseminated to understand how institutions from different countries implement AC. We interviewed 9 survey respondents and from their responses we identified four important factors that make AC successful: commitment (how the organizer and attendees participate in AC), environment (how conducive and comfortable AC is conducted), content (the discussed topics in AC and how they are presented), and objective (the main goal/s of conducting AC). We also present the format of our AC, an elective class which was evaluated during the Spring Semester 2020 (March 2020 - June 2020). Our evaluation with the attendees showed that enrollees (those who are enrolled and are required to present papers regularly) tend to be more committed in attending compared to audiences (those who are not enrolled and are not required to present papers regularly). In addition, participants tend to find papers outside their research field harder to read. Finally, we showed an improvement in the weekly number of papers read after attending AC of those who present papers regularly, and a high satisfaction rating of our AC. We summarize the areas of improvement in our AC implementation, and we encourage other institutions to evaluate their own AC in accordance with the four aforementioned factors to assess the effectiveness of their AC in reaching their goals.

D. Hill, O. Fox, A. Hager et al.

Saif S. Ahmad, M. Crittenden, P. Tran et al.

Radiotherapy is a fundamental component of treatment for the majority of patients with cancer. In recent decades, technological advances have enabled patients to receive more targeted doses of radiation to the tumor, with sparing of adjacent normal tissues. There had been hope that the era of precision medicine would enhance the combination of radiotherapy with targeted anticancer drugs; however, this ambition remains to be realized. In view of this lack of progress, the FDA–AACR–ASTRO Clinical Development of Drug–Radiotherapy Combinations Workshop was held in February 2018 to bring together stakeholders and opinion leaders from academia, clinical radiation oncology, industry, patient advocacy groups, and the FDA to discuss challenges to introducing new drug–radiotherapy combinations to the clinic. This Perspectives in Regulatory Science and Policy article summarizes the themes and action points that were discussed. Intelligent trial design is required to increase the number of studies that efficiently meet their primary outcomes; endpoints to be considered include local control, organ preservation, and patient-reported outcomes. Novel approaches including immune-oncology or DNA-repair inhibitor agents combined with radiotherapy should be prioritized. In this article, we focus on how the regulatory challenges associated with defining a new drug–radiotherapy combination can be overcome to improve clinical outcomes for patients with cancer.

Sajal Gupta, S. Desai

Motivated by previous studies in literature about the potential importance of relativistic corrections to galaxy cluster hydrostatic masses, we calculate the masses of 12 relaxed clusters (with Chandra X-ray data) using the Tolman-Oppenheimer-Volkov (TOV) equation of hydrostatic equilibrium and the ideal gas equation of state. Analytical formulae for gas density and temperature profiles for these clusters, previously derived by Vikhlinin et al (astro-ph/0507092) were used to obtain these masses. We compare the TOV-based masses with those obtained using the corresponding Newtonian equation of hydrostatic equilibrium. We find that the fractional relative difference between the two masses are negligible, corresponding to $\sim \mathcal{O}(10^{-5})$.

H. Quon, N. Vapiwala, A. Forastiere et al.

Yasser Yasami

I. Chetty, M. Martel, D. Jaffray et al.

F Camilo, D. Lorimer, P. Freire et al.

A. Rudolph, E. Prather, G. Brissenden et al.

R. Lazkoz, S. Nesseris, L. Perivolaropoulos

We compare the dark energy model constraints obtained by using recent standard ruler data (baryon acoustic oscillations (BAO) at z = 0.2 and 0.35 and cosmic microwave background (CMB) shift parameters R and la) with the corresponding constraints obtained by using recent type Ia supernovae (SnIa) standard candle data (ESSENCE+SNLS+HST from astro-ph/0701510). We find that, even though both classes of data are consistent with ΛCDM (CDM: cold dark matter) at the 2σ level, there is a systematic difference between the two classes of data. In particular, we find that for practically all values of the parameters (Ω0m,Ωb) in the 2σ range of the three-year WMAP data (WMAP3) best fit, ΛCDM is significantly more consistent with the SnIa data than with the CMB+BAO data. For example for (Ω0m,Ωb) = (0.24,0.042) corresponding to the best fit values of WMAP3, the dark energy equation of state parameterization w(z) = w0+w1(z/1+z) best fit is at a 0.5σ distance from ΛCDM (w0 = −1,w1 = 0) using the SnIa data and 1.7σ away from ΛCDM using the CMB+BAO data. There is a similar trend in the earlier data (SNLS versus CMB+BAO at z = 0.35). This trend is such that the standard ruler CMB+BAO data show a mild preference for crossing of the phantom divide line w = −1, while the recent SnIa data favor ΛCDM. Despite this mild difference in trends, we find no statistically significant evidence for violation of the cosmic distance duality relation . For example, using a prior of Ω0m = 0.24, we find η = 0.95 ± 0.025 in the redshift range 0

Edward H. Lee, J. Jersey, Carol Gifford et al.

F. Roig, D. Nesvorný, R. Gil-Hutton et al.

Abstract V-type asteroids are bodies whose surfaces are constituted of basalt. In the Main Asteroid Belt, most of these asteroids are assumed to come from the basaltic crust of Asteroid (4) Vesta. This idea is mainly supported by (i) the fact that almost all the known V-type asteroids are in the same region of the belt as (4) Vesta, i.e., the inner belt (semi-major axis 2.1 a 2.5 AU), (ii) the existence of a dynamical asteroid family associated to (4) Vesta, and (iii) the observational evidence of at least one large craterization event on Vesta's surface. One V-type asteroid that is difficult to fit in this scenario is (1459) Magnya, located in the outer asteroid belt, i.e., too far away from (4) Vesta as to have a real possibility of coming from it. The recent discovery of the first V-type asteroid in the middle belt ( 2.5 a 2.8 AU), (21238) 1995WV7 [Binzel, R.P., Masi, G., Foglia, S., 2006. Bull. Am. Astron. Soc. 38, 627; Hammergren, M., Gyuk, G., Puckett, A., 2006. ArXiv e-print, astro-ph/0609420], located at ∼2.54 AU, raises the question of whether it came from (4) Vesta or not. In this paper, we present spectroscopic observations indicating the existence of another V-type asteroid at ∼2.53 AU, (40521) 1999RL95, and we investigate the possibility that these two asteroids evolved from the Vesta family to their present orbits by a semi-major axis drift due to the Yarkovsky effect. The main problem with this scenario is that the asteroids need to cross the 3/1 mean motion resonance with Jupiter, which is highly unstable. Combining N-body numerical simulations of the orbital evolution, that include the Yarkovsky effect, with Monte Carlo models, we compute the probability that an asteroid of a given diameter D evolves from the Vesta family and crosses over the 3/1 resonance, reaching a stable orbit in the middle belt. Our results indicate that an asteroid like (21238) 1995WV7 has a low probability (∼1%) of having evolved through this mechanism due to its large size ( D ∼ 5 km ), because the Yarkovsky effect is not sufficiently efficient for such large asteroids. However, the mechanism might explain the orbits of smaller bodies like (40521) 1999RL95 ( D ∼ 3 km ) with ∼ 70 – 100 % probability, provided that we assume that the Vesta family formed ≳ 3.5 Gy ago. We estimate the debiased population of V-type asteroids that might exist in the same region as (21238) and (40521) ( 2.5 a ≲ 2.62 AU ) and conclude that about 10 to 30% of the V-type bodies with D > 1 km may come from the Vesta family by crossing over the 3/1 resonance. The remaining 70–90% must have a different origin.

S. Nesseris, L. Perivolaropoulos

The Gold06 SnIa data set recently released in astro-ph/0611572 consists of five distinct subsets defined by the group or instrument that discovered and analysed the corresponding data. These subsets are: the SNLS subset (47 SnIa), the HST subset (30 SnIa), the HZSST subset (41 SnIa), the SCP subset (26 SnIa) and the low redshift (LR) subset (38 SnIa). These subsets sum up to the 182 SnIa of the Gold06 data set. We use Monte Carlo simulations to study the statistical consistency of each one of the above subsets with the full Gold06 data set. In particular, we compare the best fit w(z) parameters (w0, w1) obtained by subtracting each one of the above subsets from the Gold06 data set (subset truncation), with the corresponding best fit parameters (w0r, w1r) obtained by subtracting the same number of randomly selected SnIa from the same redshift range of the Gold06 data set (random truncation). We find that the probability for (w0r, w1r) = (w0, w1) is large for the Gold06 minus SCP (Gold06-SCP) truncation but is less than 5% for the Gold06-SNLS, Gold06-HZSST and Gold06-HST truncations. This result implies that the Gold06 data set is not statistically homogeneous. By comparing the values of the best fit (w0, w1) for each subset truncation we find that the tension among subsets is such that the SNLS and HST subsets are statistically consistent with each other and ‘pull’ towards ΛCDM (w0 = −1, w1 = 0) while the HZSST subset is statistically distinct and strongly ‘pulls’ towards a varying w(z) crossing the line w = −1 from below (w0 0). We also isolate six SnIa that are mostly responsible for this behaviour of the HZSST subset.

N. Chamel

The outer layers of a neutron star are supposed to be formed of a solid Coulomb lattice of neutron rich nuclei. At densities above neutron drip density (about one thousandth of nuclear saturation density), this lattice is immersed in a neutron fluid. Bragg scattering of those dripped neutrons by the nuclei which has been usually neglected is investigated, within a simple mean field model with Bloch type boundary conditions. The main purpose of this work is to provide some estimates for the entrainment coefficients, as required for hydrodynamical two fluid simulations of neutron star crust [nucl-th/0402057, astro-ph/0408083], which relate the momentum of one fluid to the particle currents of the other two fluids [Sov. Phys. JETP 42 (1976) 164]. The implications for the equilibrium neutron star crust structure are also briefly discussed.

K. Jonsell, B. Edvardsson, B. Gustafsson et al.

We have derived abundances of O, Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Fe, Ni and Ba for 43 metal-poor field stars, mostly stars at the turn-off point and on the subgiant branch, in the interval ${-}3.0{<}$[Fe/H]${<}{-}0.4$. The analysis is differential relative to the Sun. Oxygen abundances, with consideration of NLTE effects, were derived from the OI 777.4 nm triplet lines. We find [O/Fe] to gradually increase with decreasing [Fe/H], though considerably slower than has earlier been obtained from OH lines in the UV. A scatter in [O,Mg,Ca,Ti/Fe] at a given [Fe/H] is found and we argue that this scatter is partly real. The deviations from the mean trends of abundance ratios vs [Fe/H] are found to correlate in non-trivial ways for different abundances. Similar trends are found from results of accurate studies by other groups. This seems to give further evidence for the hypothesis that the stars once formed in different subsystems, with different star-formation rates. The paper is in press in A&A, may be obtained as astro-ph/0505118.

A. Ashoorioon, J. Hovdebo, R. Mann

Abstract One of the firm predictions of inflationary cosmology is the consistency relation between scalar and tensor spectra. It has been argued that such a relation—if experimentally confirmed—would offer strong support for the idea of inflation. We examine the possibility that trans-Planckian physics violates the consistency relation in the framework of inflation with a cut-off proposed in [ astro-ph/0009209 ]. We find that despite the ambiguity that exists in choosing the action, Planck scale physics modifies the consistency relation considerably. It also leads to the running of the spectral index. For modes that are larger than our current horizon, the tensor spectral index is positive. For a window of k values with amplitudes of the same order of the modes which are the precursor to structure formation, the behavior of tensor spectral index is oscillatory about the standard quantum field theory result, taking both positive and negative values. There is a hope that in the light of future experiments, one can verify this scenario of short distance physics.

Laila Alabidi, D. Lyth

The survey of models in astro-ph/0510441 is updated. For the first time, a large fraction of the models is ruled out at more than 3σ.

D. Jauncey, J. Macquart

The intra-day variable source 0917+624 displays annual changes in its timescale of variability. This is explained in terms of a scintillation model in which changes in the variability timescale are due to changes in the relative velocity of the scintillation pattern as the Earth orbits the sun. (see also astro-ph/0102050)

S. Rhie

It has been conjectured (astro-ph/0103463) that a gravitational lens consisting of n point masses can not produce more than 5(n-1) images as is known to be the case for n = 2 and 3. The reasoning is based on the number of finite limit points 2(n-1) which we believe to set the maximum number of positive images and the fact that the number of negative images exceeds the number of positive images by (n-1). It has been known that an n-point lens system (n\ge 3) can produce (3n+1) images and so has been an explicit lens configuration with (3n+1) images. We start with the well-known n-point lens configuration that produces (3n+1) images and produce (2n-1) extra images by adding a small (n+1)-th mass so that the resulting (n+1)-point lens configuration has (2n) discrete limit points and produces 5n images of a source. It still remains to confirm in abstraction that the maximum number of positive image domains of a caustic domain is bounded by the number of the limit points.

P. Schady, M. Pasquale, M.J.Page et al.

%auto-ignore This paper has been withdrawn by the authors due to dublicate submission. To download the paper please go to astro-ph/0611081