标题 关键字 摘要 作者 全部

 第1页/共100条 每页显示 5 10 20 条
 Physics , 2015, Abstract: We present a method for modeling the evolution of detached double white dwarf (DWD) binaries hosting helium donors from the end of the common envelope (CE) phase to the onset of Roche Lobe overflow (RLOF). This is achieved by combining detailed stellar evolution calculations of extremely low mass (ELM) helium WDs possessing hydrogen envelopes with the the orbital shrinking of the binary driven by gravitational radiation. We show that the consideration of hydrogen fusion in these systems is crucial, as a significant fraction ($\approx$50%) of future donors are expected to still be burning when mass transfer commences. We apply our method to two detached eclipsing DWD systems, SDSS J0651+2844 and NLTT-11748, in order to demonstrate the effect that carbon-nitrogen-oxygen (CNO) flashes have on constraining the evolutionary history of such systems. We find that when CNO flashes are absent on the low mass WD ($M_{2}$ < $0.18 M_{\odot}$), such as in NLTT-11748, we are able to self consistently solve for the donor conditions at CE detachment given a reliable cooling age from the massive WD companion. When CNO flashes occur (0.18 $M_{\odot}$ < $M_{2}$ < 0.36 $M_{\odot}$), such as in SDSS J0651+2844, the evolutionary history is eradicated and we are unable to comment on the detachment conditions. We find that for any donor mass our models are able to predict the conditions at reattachment and comment on the stabilizing effects of hydrogen envelopes. This method can be applied to a population of detached DWDs with measured donor radii and masses.
 International Journal of Conflict and Violence , 2010, Abstract: An examination of potential outgroup-focused predictors of group-based guilt relating to past colonial conflicts involving Portugal and the Netherlands, specifically, the role of the perceptions of the ingroup towards the victimized outgroup, as well as on outgroup identification and meta-perceptions (i.e. the ingroup's beliefs regarding the outgroup's perceptions of it). Using Structural Equation Modeling in a Portuguese sample (N = 178) and a Dutch sample (N = 157), we found that the experience of group-based guilt due to colonial conflicts can be positively predicted by outgroup perceptions and outgroup identification (Dutch sample only). Meta-perceptions were a negative predictor of group-based guilt (Dutch sample only). Furthermore, our results show that group-based guilt is positively associated with compensatory behavioral intentions and perceived importance of remembering past colonial conflicts. Results point to the important role of outgroup-focused variables in shaping group-based guilt experiences relating to past conflicts between groups. The findings suggest possible avenues of further research and ways to improve intergroup relations following conflict.
 Physiology and Pharmacology , 2013, Abstract: Temperament (Mizaj), as an individual factor, has great importance in traditional medicine and its use in diagnosis and treatment of diseases, as well as the individual lifestyle is very common. Since medicine moves toward Personalized Medicine, the root of individual differences will find its position in different aspects of medicine in early future. In traditional medicine, temperament is defined as the only cause of individual differences and this scientific principle in the near future will be highly regarded. Recent studies also indicate the important role of temperament in body functions. Association of temperament with autonomic and immune systems, blood groups and various diseases also confirms this role. The present study provides a scheme of the history of temperament science, current status and its future, and tries to map a correct portray of temperament trend from the past to the future.
 Mathematics , 2010, Abstract: We show how the shared information between the past and future---the excess entropy---derives from the components of directional information stored in the present---the predictive and retrodictive causal states. A detailed proof allows us to highlight a number of the subtle problems in estimation and analysis that impede accurate calculation of the excess entropy.
 Physics , 2009, DOI: 10.1088/0004-637X/698/1/666 Abstract: We show how the recent discovery of a likely close white dwarf companion to the well known star Regulus, one of the brightest stars in the sky, leads to considerable insight into the prior evolutionary history of this star, including the cause of its current rapid rotation. We infer a relatively narrow range for the initial masses of the progenitor system: M_{10} = 2.3 +/- 0.2 M_sun and M_{20} = 1.7 +/- 0.2 M_sun, where M_{10} and M_{20} are the initial masses of the progenitors of the white dwarf and Regulus, respectively. In this scenario, the age of the Regulus system would exceed 1 Gyr. We also show that Regulus, with a current orbital period of 40 days, has an interesting future ahead of it. This includes (i) a common envelope phase, and, quite possibly, (ii) an sdB phase, followed by (iii) an AM CVn phase with orbital periods < 1 hr. Binary evolution calculations are presented in support of this scenario. We also discuss alternative possibilities, emphasizing the present uncertainties in binary evolution theory. Thus, this one particular star system illustrates many different aspects of binary stellar evolution.
 Aephraim M. Steinberg Physics , 2003, Abstract: This chapter is based on a talk given at the Science and Ultimate Reality meeting in March, 2002, in honour of John Archibald Wheeler. In it, I discuss some questions related to what can and cannot be said about the history of a quantum mechanical system. Relying heavily on the weak- measurement formalism of Aharonov and coworkers, I argue that there is much to be learned about a system based both on its preparation and on subsequent postselection. This is illustrated with examples from a number of past, present, and future experiments from our lab, ranging from tests of quantum "paradoxes" to studies of nonlocality to non-deterministic implementations of logic operations on quantum information. The connection between weak measurements and generalized probability theory is discussed, along with some of the counterintuitive features of these "probabilities." Conclusions are for the most part left to the reader.
 E. Predazzi Physics , 1998, Abstract: Hadronic diffraction has become a hot and fashionable subject in recent years due to the great interest triggered by the HERA and Tevatron data. These data have helped to put the field in a different perspective paving the road to a hopefully more complete understanding than hitherto achieved. The forthcoming data in the next few years from even higher energies (LHC) promise to sustain this interest for a long time. It is, therefore, necessary to provide the younger generations with as complete as possible discussion of the main developments that have marked the growth of high energy diffractive physics in the past and to assess the present state of the art. For this reason, this part will be by far the largest. The analysis of the relationship between conventional diffractive physics and the low-x physics from deep inelastic scattering will allow us also to review the instruments which could help to understand the developments we can expect from the future.
 Physics , 2000, DOI: 10.1063/1.1363525 Abstract: The past, present and future of cosmic microwave background (CMB) anisotropy research is discussed, with emphasis on the Boomerang and Maxima balloon experiments. These data are combined with large scale structure (LSS) information and high redshift supernova (SN1) observations to explore the inflation-based cosmic structure formation paradigm. Here we primarily focus on a simplified inflation parameter set, {omega_b,omega_{cdm},Omega_{tot}, Omega_Q,w_Q, n_s,tau_C, sigma_8}. After marginalizing over the other cosmic and experimental variables, we find the current CMB+LSS+SN1 data gives Omega_{tot}=1.04\pm 0.05, consistent with (non-baroque) inflation theory. Restricting to Omega_{tot}=1, we find a nearly scale invariant spectrum, n_s =1.03 \pm 0.07. The CDM density, omega_{cdm}=0.17\pm 0.02, is in the expected range, but the baryon density, omega_b=0.030\pm 0.004, is slightly larger than the current nucleosynthesis estimate. Substantial dark energy is inferred, Omega_Q\approx 0.68\pm 0.05, and CMB+LSS Omega_Q values are compatible with the independent SN1 estimates. The dark energy equation of state, parameterized by a quintessence-field pressure-to-density ratio w_Q, is not well determined by CMB+LSS (w_Q<-0.3 at 95%CL), but when combined with SN1 the resulting w_Q<-0.7 limit is quite consistent with the w_Q=-1 cosmological constant case. Though forecasts of statistical errors on parameters for current and future experiments are rosy, rooting out systematic errors will define the true progress.
 Revista de Metalurgia , 2005, Abstract: Intermetallics have seen extensive world-wide attention over the past decades. For the most part these studies have examined multi-phase aluminide based alloys, because of their high stiffness, combined with reasonable strength and ductility, good structural stability and oxidation resistance, and attempted to improve current Ni-base superalloys, Ti-base alloys, or Fe-base stainless steels for structural aerospace applications. The current status of development and application of such materials is briefly reviewed. Future developments are taking intermetallics from the realm of "improved high-temperature but low-ductility metallic alloys" into the realm of "improved aggressive-environment, high-toughness ceramic-like alloys". Such evolution will be outlined. Durante los últimos décadas ha habido un desarrollo de los intermetálicos, sobre todo por aplicaciones estructurales a alta temperatura en aplicaciones aeroespaciales, donde, por su rigidez alta, en combinación con una resistencia mecánica y ductilidad razonable, su buena estabilidad estructural y resistencia a la oxidación, han sido vistos como versiones avanzadas y mejoradas de las aleaciones metálicas como, por ejemplo, las superaleaciones a base de nitrógeno y las aleaciones de titanio. Se discute el desarrollo importante durante las últimas décadas, y también los nuevos desarrollos probables durante los próximos a os. Se podrían ver los intermetálicos como versiones mejoradas de los cerámicos.
 Maurice H. P. M. van Putten Physics , 2001, DOI: 10.1088/0264-9381/19/6/101 Abstract: Numerical relativity describes a discrete initial value problem for general relativity. A choice of gauge involves slicing space-time into space-like hypersurfaces. This introduces past and future gauge relative to the hypersurface of present time. Here, we propose solving the discretized Einstein equations with a choice of gauge in the future and a dynamical gauge in the past. The method is illustrated on a polarized Gowdy wave.
 第1页/共100条 每页显示 5 10 20 条