298 research outputs found
Study of the Hindrance Effect in Sub-barrier Fusion Reactions
We have measured the fusion cross sections of the 12C(13C, p)24Na reaction
through off-line measurement of the beta-decay of 24Na using the beta-gamma
coincidence method. Our new measurements in the energy range of Ec.m. = 2.6-3.0
MeV do not show an obvious S-factor maximum but a plateau. Comparison between
this work and various models is presented.Comment: 3 pages, 3 figures, Talk at the "10th International Conference on
Nucleus-Nucleus Collisions", Beijing, 16-21 August 200
Constitutive Equations and Processing Maps for 49MnVS3 Non-Quenched and Tempered Steel
Flow stress variations of 49MnVS3 non-quenched
and tempered steel are studied in isothermal compression
tests on a Gleeble-1500D thermal simulated
test machine at a deformation temperatures
of 950, 1000, 1150, and 1200° C, and strain rates
of 0.1, 1, 5, and 10 s⁻¹, with obtaining the strain
hardening exponent n and deformation activation
energy Q of the alloy. Thus, the constitutive
equations and processing maps of compression
flow behavior for 49MnVS3 non-quenched and
tempered steel at high temperatures are established.
It shows that the peak stress is shownto
significantly reduced with a decrease in the
strain rate and increase in deformation temperature
when the alloy deforms at high temperature,
and the deformation activation energy is
350.98 kJ/mol. When the true strain of
49MnVS3 non-quenched and microalloyed steel
high-temperature deformation is 0.5, the optimum
process parameters of the alloy are determined
to be 1150–1200° C for the deformation
temperature and 2–10 s⁻¹ for the strain rate,
based on the criterion that the process parameters
of higher power dissipation efficiency values
should be chosen in the dynamic
recrystallization region as the best processing
technology.Изменение напряжения течения незакаленной и закаленной стали 49MnVS3 исследовали путем проведения испытаний на изотермическое сжатие на установке Gleeble-1500D, моделирующей высокотемпературные условия, при температурах деформации 950, 1000, 1150, 1200° C и скоростях деформации 0,1; 1; 5 и 10 c⁻¹ с показателем степени деформационного упрочнения n и значением энергии активации деформации сплава Q. Установлены определяющие уравнения и схемы обработки компрессионного режима течения для незакаленной и закаленной стали 49MnVS3 при высокой температуре. Анализ уравнений показал, что максимальное значение напряжения значительно уменьшается при снижении скорости деформации и повышении температуры деформации, если сплав подвергается деформации при высокой температуре, а значение энергии активации деформации составляет 350,98 кДж/моль. Если значения истинной деформации незакаленной стали 49MnVS3 и высокотемпературной деформации микролегированной стали составляют 0,5, то оптимальные параметры процесса обработки сплава определяются при температуре деформирования 1150…1200° C и скорости деформации 2…10 c⁻¹ на основе критерия, который способствует отбору параметров с более высокой эффективностью рассеивания мощности в области динамической рекристаллизации в качестве оптимальной технологии обработки.Зміну напруження течії незагартованої і загартованої сталі 49MnVS3 досліджували шляхом проведення випробувань на ізотермічний стиск на установці Gleeble-1500D, що моделює високотемпературні умови, за температур деформації 950, 1000, 1150, 1200° C та швидкості деформації 0,1; 1; 5 і 10 c⁻¹ із показником степеня деформаційного зміцнення n і значенням енергії активації деформації сплаву Q. Установлено визначальні рівняння і схеми обробки компресійного режиму течії для незагартованої і загартованої сталі 49MnVS3 за високої температури. Аналіз рівнянь показав, що максимальне значення напруження значно зменшується зі зниженням швидкості деформації і підвищенні температури деформації, якщо сплав зазнає деформації за високої температури, а значення енергії активації деформації дорівнює 350,98 кДж/моль. Якщо значення істинної деформації незагартованої сталі 49MnVS3 і високотемпературної деформації мікролегованої сталі дорівнюють 0,5, то оптимальні параметри процесу обробки сплаву визначаються за температури деформування 1150...1200° C і швидкості деформації 2...10 c⁻¹ на основі критерію, який сприяє відбору параметрів із більш високою ефективністю розсіяння потужності в області динамічної рекристалізації як оптимальної технології обробки
Projected SO(5) Hamiltonian for Cuprates and Its Applications
The projected SO(5) (pSO(5)) Hamiltonian incorporates the quantum spin and
superconducting fluctuations of underdoped cuprates in terms of four bosons
moving on a coarse grained lattice. A simple mean field approximation can
explain some key feautures of the experimental phase diagram: (i) The Mott
transition between antiferromagnet and superconductor, (ii) The increase of T_c
and superfluid stiffness with hole concentration x and (iii) The increase of
antiferromagnetic resonance energy as sqrt{x-x_c} in the superconducting phase.
We apply this theory to explain the ``two gaps'' problem found in underdoped
cuprate Superconductor-Normal- Superconductor junctions. In particular we
explain the sharp subgap Andreev peaks of the differential resistance, as
signatures of the antiferromagnetic resonance (the magnon mass gap). A critical
test of this theory is proposed. The tunneling charge, as measured by shot
noise, should change by increments of Delta Q= 2e at the Andreev peaks, rather
than by Delta Q=e as in conventional superconductors.Comment: 3 EPS figure
A new ghost cell/level set method for moving boundary problems:application to tumor growth
In this paper, we present a ghost cell/level set method for the evolution of interfaces whose normal velocity depend upon the solutions of linear and nonlinear quasi-steady reaction-diffusion equations with curvature-dependent boundary conditions. Our technique includes a ghost cell method that accurately discretizes normal derivative jump boundary conditions without smearing jumps in the tangential derivative; a new iterative method for solving linear and nonlinear quasi-steady reaction-diffusion equations; an adaptive discretization to compute the curvature and normal vectors; and a new discrete approximation to the Heaviside function. We present numerical examples that demonstrate better than 1.5-order convergence for problems where traditional ghost cell methods either fail to converge or attain at best sub-linear accuracy. We apply our techniques to a model of tumor growth in complex, heterogeneous tissues that consists of a nonlinear nutrient equation and a pressure equation with geometry-dependent jump boundary conditions. We simulate the growth of glioblastoma (an aggressive brain tumor) into a large, 1 cm square of brain tissue that includes heterogeneous nutrient delivery and varied biomechanical characteristics (white matter, gray matter, cerebrospinal fluid, and bone), and we observe growth morphologies that are highly dependent upon the variations of the tissue characteristics—an effect observed in real tumor growth
Fusion measurements of 12C+12C at energies of astrophysical interest
The cross section of the 12C+12C fusion reaction at low energies is of paramount importance for models of stellar nucleosynthesis in different astrophysical scenarios, such as Type Ia supernovae and Xray superbursts, where this reaction is a primary route for the production of heavier elements. In a series of experiments performed at Argonne National Laboratory, using Gammasphere and an array of Silicon detectors, measurements of the fusion cross section of 12C+12C were successfully carried out with the γ and charged-particle coincidence technique in the center-of-mass energy range of 3-5 MeV. These were the first background-free fusion cross section measurements for 12C+12C at energies of astrophysical interest. Our results are consistent with previous measurements in the high-energy region; however, our lowest energy measurement indicates a fusion cross section slightly lower than those obtained with other techniques
How well do we understand the reaction rate of C burning?
Carbon burning plays a crucial role in stellar evolution, where this reaction is an important route for the production of heavier elements. A particle-γ coincidence technique that minimizes the backgrounds to which this reaction is subject and provides reliable cross sections has been used at the Argonne National Laboratory to measure fusion cross-sections at deep sub-barrier energies in the 12C+12C system. The corresponding excitation function has been extracted down to a cross section of about 6 nb. This indicates the existence of a broad S-factor maximum for this system. Experimental results are presented and discussed
Measurements of the observed cross sections for exclusive light hadrons containing at , 3.650 and 3.6648 GeV
By analyzing the data sets of 17.3, 6.5 and 1.0 pb taken,
respectively, at , 3.650 and 3.6648 GeV with the BES-II
detector at the BEPC collider, we measure the observed cross sections for
, , ,
and at the three energy
points. Based on these cross sections we set the upper limits on the observed
cross sections and the branching fractions for decay into these
final states at 90% C.L..Comment: 7 pages, 2 figure
Partial wave analysis of J/\psi \to \gamma \phi \phi
Using events collected in the BESII detector, the
radiative decay is
studied. The invariant mass distribution exhibits a near-threshold
enhancement that peaks around 2.24 GeV/.
A partial wave analysis shows that the structure is dominated by a
state () with a mass of
GeV/ and a width of GeV/. The
product branching fraction is: .Comment: 11 pages, 4 figures. corrected proof for journa
Direct Measurements of Absolute Branching Fractions for D0 and D+ Inclusive Semimuonic Decays
By analyzing about 33 data sample collected at and around 3.773
GeV with the BES-II detector at the BEPC collider, we directly measure the
branching fractions for the neutral and charged inclusive semimuonic decays
to be and , and determine the ratio of the two branching
fractions to be
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