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Search Results: 1 - 10 of 323909 matches for " Hu J. "
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Estigma e identidad. Una aproximación a la cuestión juvenil
Huáscar J. Cajías
Ultima Década , 1999,
Abstract:
Uncertainty of the CO2 threshold for melting a hard Snowball Earth
Y. Hu,J. Yang
Climate of the Past Discussions , 2010, DOI: 10.5194/cpd-6-1337-2010
Abstract: One of the critical issues of the Snowball Earth hypothesis is how high level of CO2 is required for triggering the deglaciation. Using Community Atmospheric Model version 3 (CAM3), we study the problem for the CO2 threshold. Our simulations show large differences from previous results (Pierrehumbert, 2004, 2005). At 0.2 bars of CO2, the January maximum near-surface temperature is about 268 K, about 13 K higher than that in Pierrehumbert (2004, 2005), but lower than the value of 270 K for 0.1 bar of CO2 in Le Hir et al. (2007). It is found that the diversity of simulation results is mainly due to model sensitivity of greenhouse effect and longwave cloud forcing to increasing CO2. At 0.2 bar of CO2, CAM3 yields 117 Wm 2 of clear-sky greenhouse effect and 32 Wm 2 of longwave cloud forcing, versus only about 77 Wm 2 and 10.5 Wm 2 in Pierrehumbert (2004, 2005), respectively. CAM3 has comparable clear-sky greenhouse effect to that in Le Hir et al. (2007), but lower longwave cloud forcing. CAM3 also produces much stronger Hadley cells than in Pierrehumbert (2005).
The Effects of Process Parameters on Evolutions of Thermodynamics and Microstructures for Composite Extrusion of Magnesium Alloy
H.-J. Hu
Advances in Materials Science and Engineering , 2013, DOI: 10.1155/2013/259594
Abstract: To research the effects of process parameters on evolutions of extrusion force and temperature rise and microstructures for composite extrusion of magnesium alloy which includes initial extrusion and shearing process subsequently and is shortened for “ES” in this paper, the ES extrusion process has been researched by using finite element modeling (FEM) technology. The rules of temperature rise and the extrusion force varying with process parameters have been developed. The thermal-mechanical coupling finite element models including the geometric and FEM models and solution conditions were applied to calculate the effective strain and temperature and extrusion force during ES extrusion. The maximum temperature rises in the billets do not increase with billet temperature rising. The temperature of rod surface increased continuously with development of ES extrusion. The evolutions of extrusion load curve and effective stress and temperature can be divided into three stages obviously. Extrusion experiments have been constructed to validate the FEM models with different process conditions. The simulation results and microstructure observation showed that ES process can introduce compressive and accumulated shear strain into the magnesium alloy. The ES extrusion would cause severe plastic deformation and improve the dynamic recrystallization during ES extrusion. The microstructures show that ES is an efficient and inexpensive grain refinement method for magnesium alloys. 1. Introduction The specific strength of magnesium alloys is high, and use of magnesium parts would cause weight saving of around 30% and 70% compared to aluminum and steel, respectively. Currently, market for magnesium alloys is fast expanding from automobiles to electronic applications. Structural applications normally require energy absorption materials with reasonable elongation, high yield strength, and high impact energy. In recent years, bulk nanostructure materials processed by severe plastic deformation (SPD) such as equal channel angular extrusion (ECAE) have attracted the growing interest of specialists in materials science. The important phenomena observed in of ECAE process for magnesium alloys are the DRX (dynamic recrystallization) and DRV (dynamic recovery), which could improve the workability of the material at elevated temperatures. M. Furui et al. have researched the influences of preliminary extrusion conditions on the superplastic properties of a magnesium alloy two-phase Mg-8% Li processed by ECAP in three different conditions including cast condition, cast + extrude
MICROSTRUCTURAL MODEL OF GATORIZED WASPALOY IN THE ISOTHERMAL FORGING PROCESS
JP Hu,
J.P.
,Hu

金属学报(英文版) , 2001,
Abstract: A microstructural model, which was to predict the evolution of microstructure of Gatorized Waspeloy in the isothermal forcing process, was developed in terms of dynamic recrystallization and grain growth. Three steps of experiment were conducted during developing the model: (1) .Specimens were compressed in M FS testing machine; (2) Dynamic recrystallization and grain growth were discussed; (3) Dynamic recrys- tallization model and grain growth mode were set up. The agreement of simulated results and experimental data is fine.
Color-Tunable Etalons Assembled from Poly?(N-Isopropylacrylamide) Based Microgels
Liang Hu,Michael J. Serpe
Polymers , 2012, DOI: 10.3390/polym4010134
Abstract: Photonic materials (PMs) that are capable of manipulating and controlling light in systems have immense potential for the computing and communications industries. These materials are formed by assembling components of differing refractive indices in a periodic array. Light then interacts with this assembly, which results in constructive and destructive interference, and hence color. While many three-dimensional PMs have been reported, and have the most potential for the applications mentioned above, one-dimensional PMs have a multitude of potential uses, e.g., light filtration. In this review, we focus on one-dimensional PMs; specifically poly ( N-isopropylacrylamide) microgel based etalons. The etalons can be fabricated to exhibit a single bright color, and because the diameter of the microgels is dependent on temperature and pH, the mirror-mirror spacing can be dynamically tuned; therefore the etalon’s color is dynamically tunable.
Klein-Gordon equations for toroidal hydromagnetic waves in an axi-symmetric field
J. F. McKenzie,Q. Hu
Annales Geophysicae (ANGEO) , 2010,
Abstract: In this paper we develop the hydromagnetic wave equations for toroidal Alfvén waves in a background axi-symmetric magnetic field. In the case where spatial variations are directed along the ambient magnetic field direction, the equations can be cast in a Klein-Gordon form in which the adiabatic-geometric amplitude factor of the perturbations varies as √ρL5sin5θ along a magnetic field line (where θ is colatitude and L the L-shell number) and the cut-off frequency, associated with the Klein-Gordon form, displays an astonishing variation with distance along a field line (see Eqs. 35 and 37 of the text), in the case of a dipole magnetic field. We compute the eigenvalues and eigenfunctions for the Earth's dipole field which are relevant to geomagnetic pulsations.
Statistical Redundancy Testing for Improved Gene Selection in Cancer Classification Using Microarray Data
Simin Hu,J. Sunil Rao
Cancer Informatics , 2007,
Abstract: In gene selection for cancer classifi cation using microarray data, we define an eigenvalue-ratio statistic to measure a gene’s contribution to the joint discriminability when this gene is included into a set of genes. Based on this eigenvalueratio statistic, we define a novel hypothesis testing for gene statistical redundancy and propose two gene selection methods. Simulation studies illustrate the agreement between statistical redundancy testing and gene selection methods. Real data examples show the proposed gene selection methods can select a compact gene subset which can not only be used to build high quality cancer classifiers but also show biological relevance.
Baryonic Features in the Matter Transfer Function
Daniel J. Eisenstein,Wayne Hu
Physics , 1997, DOI: 10.1086/305424
Abstract: We provide scaling relations and fitting formulae for adiabatic cold dark matter cosmologies that account for all baryon effects in the matter transfer function to better than 10% in the large-scale structure regime. They are based upon a physically well-motivated separation of the effects of acoustic oscillations, Compton drag, velocity overshoot, baryon infall, adiabatic damping, Silk damping, and cold-dark-matter growth suppression. We also find a simpler, more accurate, and better motivated form for the zero baryon transfer function than previous works. These descriptions are employed to quantify the amplitude and location of baryonic features in linear theory. While baryonic oscillations are prominent if the baryon fraction exceeds $\Omega_0 h^2 + 0.2$, the main effect in more conventional cosmologies is a sharp suppression in the transfer function below the sound horizon. We provide a simple but accurate description of this effect and stress that it is not well approximated by a change in the shape parameter $\Gamma$.
Evidence for horizon-scale power from CMB polarization
Michael J. Mortonson,Wayne Hu
Physics , 2009, DOI: 10.1103/PhysRevD.80.027301
Abstract: The CMB temperature power spectrum offers ambiguous evidence for the existence of horizon-scale power in the primordial power spectrum due to uncertainties in spatial curvature and the physics of cosmic acceleration as well as the observed low quadrupole. Current polarization data from WMAP provide evidence for horizon-scale power that is robust to these uncertainties. Polarization on the largest scales arises mainly from scattering at z<6 when the universe is fully ionized, making the evidence robust to ionization history variations at higher redshifts as well. A cutoff in the power spectrum is limited to C=k_C/10^{-4} Mpc^{-1}<5.2 (95% CL) by polarization, only slightly weaker than joint temperature and polarization constraints in flat LCDM (C<4.2). Planck should improve the polarization limit to C<3.6 for any model of the acceleration epoch and ionization history as well as provide tests for foreground and systematic contamination.
Observational Limits on Patchy Reionization: Implications for B-modes
Michael J. Mortonson,Wayne Hu
Physics , 2010, DOI: 10.1103/PhysRevD.81.067302
Abstract: The recent detection of secondary CMB anisotropy by the South Pole Telescope places a conservative bound on temperature fluctuations from the optical depth-modulated Doppler effect of T_{3000} < sqrt{13} microK at multipoles l~3000. This bound is the first empirical constraint on reionization optical depth fluctuations at arcminute scales, tau_{3000} = 0.001 T_{3000}/microK, implying that these fluctuations are no more than a few percent of the mean. Optical depth modulation of the quadrupole source to polarization generates B-modes that are correspondingly bounded as B_{3000} = 0.003 T_{3000}. The maximal extrapolation to the l~100 gravitational wave regime yields B_{100} = 0.1 T_{3000} and remains in excess of gravitational lensing if the effective comoving size of the ionizing regions is R > 80 Mpc. If patchy reionization is responsible for much of the observed arcminute scale temperature fluctuations, current bounds on B_{100} already require R < 200 Mpc and can be expected to improve rapidly. Frequency separation of thermal Sunyaev-Zel'dovich contributions to the measured secondary anisotropy would also substantially improve the limits on optical depth fluctuations and B-modes from reionization.
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