2,897 research outputs found
Suppression of the water ice and snow albedo feedback on planets orbiting red dwarf stars and the subsequent widening of the habitable zone
M-stars comprise 80% of main-sequence stars, and so their planetary systems
provide the best chance for finding habitable planets, i.e.: those with surface
liquid water. We have modelled the broadband albedo or reflectivity of water
ice and snow for simulated planetary surfaces orbiting two observed red dwarf
stars (or M-stars) using spectrally resolved data of the Earth's cryosphere.
The gradual reduction of the albedos of snow and ice at wavelengths greater
than 1 ?m, combined with M-stars emitting a significant fraction of their
radiation at these same longer wavelengths, mean that the albedos of ice and
snow on planets orbiting M-stars are much lower than their values on Earth. Our
results imply that the ice/snow albedo climate feedback is significantly weaker
for planets orbiting M-stars than for planets orbiting G-type stars such as the
Sun. In addition, planets with significant ice and snow cover will have
significantly higher surface temperatures for a given stellar flux if the
spectral variation of cryospheric albedo is considered, which in turn implies
that the outer edge of the habitable zone around M-stars may be 10-30% further
away from the parent star than previously thought.Comment: Final accepted by Astrobiology, 20 pages (double spaced), 3 figures
include
M-flation and its spectators
M-flation is an implementation of assisted inflation, in which the inflaton
fields are three N_c x N_c non-abelian hermitean matrices. The model can be
consistently truncated to an effectively single field inflation model, with all
``spectator'' fields fixed at the origin. We show that starting with random
initial conditions for all fields the truncated sector is not a late-time
attractor, but instead the system evolves towards quadratic assisted inflation
with all fields mass degenerate. Demanding the energy density during inflation
to be below the effective quantum gravity scale, we find that the number of
fields, and thus the assisted effect, is bounded N_c < 10^2.Comment: 26 pages, published versio
Background field quantization and non-commutative Maxwell theory
We quantize non-commutative Maxwell theory canonically in the background
field gauge for weak and slowly varying background fields. We determine the
complete basis for expansion under such an approximation. As an application, we
derive the Wigner function which determines the leading order high temperature
behavior of the perturbative amplitudes of non-commutative Maxwell theory. To
leading order, we also give a closed form expression for the distribution
function for the non-commutative gauge theory at high temperature.Comment: 9 pages, title slightly modified, to appear in Physics Letters
Diagnostic for Dilaton Dark Energy
diagnostic can differentiate between different models of dark energy
without the accurate current value of matter density. We apply this geometric
diagnostic to dilaton dark energy(DDE) model and differentiate DDE model from
LCDM. We also investigate the influence of coupled parameter on the
evolutive behavior of with respect to redshift . According to the
numerical result of , we get the current value of equation of state
=-0.952 which fits the WMAP5+BAO+SN very well.Comment: 6 pages and 6 figures
Examples of M5-Brane Elliptic Genera
We determine the modified elliptic genus of an M5-brane wrapped on various
one modulus Calabi-Yau spaces, using modular invariance together with some
known Gopakumar-Vafa invariants of small degrees. As a bonus, we find
nontrivial relations among Gopakumar-Vafa invariants of different degrees and
genera from modular invariance.Comment: 13 page
The Trispectrum in the Multi-brid Inflation
The trispectrum is at least as important as the bispectrum and its size can
be characterized by two parameters and . In this short
paper, we focus on the Multi-brid inflation, in particular the two-brid
inflation model in arXiv.0805.0974, and find that is always
positive and roughly equals to for the low scale
inflation, but can be negative or positive and its order of magnitude
can be the same as that of or even largerComment: 12 pages; minor correction, refs added; further refs added, version
for publication in JCA
Construction and Verification of the Constitutive Model of Pure Copper Deformation at Elevated Temperatures
The deformation behavior of pure copper was studied in hot compression tests in the temperature range of 773–1173 K and strain rate interval of 0.001–1.0 s⁻¹, the corresponding flow stress curves were plotted. The new method to calculate critical and saturation stresses was devised, quantitative analysis of strain hardening and dynamic softening was presented, a three-stage constitutive model was constructed to predict the flow stress of pure copper. As predicted and measured flow stress comparison indicate, the physical constitutive model can accurately characterize hot deformation of pure copper. With dynamic recovery and/or recrystallization. Numerical simulation of an upsetting process is carried out by implementing the constitutive model into commercial software. This model can be put to practical use and be quite promising for improving efficiency of a hot forging process for pure copper components.Изучено деформационное поведение чистой меди при испытании горячих проб на сжатие в диапазоне температур 773 1173 К и скорости деформации 0.001–1.0 с⁻¹, построены соответствующие кривые напряжения пластического течения. Разработан новый метод расчета критического напряжения и напряжения насыщения, представлен количественный анализ деформационного упрочнения и динамического разупрочнения, построена трехступенчатая определяющая модель прогнозирования напряжения пластического течения чистой меди. Как показывает сравнение прогнозируемого и измеренного напряжений пластического течения, с помощью такой модели можно точно описать горячее деформирование чистой меди при динамическом возврате и/или рекристаллизации. Выполнено численное моделирование процесса высадки путем реализации данной модели в рамках коммерческого программного обеспечения. Модель весьма перспективна и может использоваться для повышения эффективности процесса горячей ковки деталей из чистой меди.Вивчено деформаційне поведінку чистої міді при випробуванні гарячих проб на стиск в діапазоні температур 773-1173 К і швидкості деформації 0.001–1.0 с⁻¹, побудовані відповідні криві напружень пластичної течії. Розроблено новий метод розрахунку критичної напруги і напруги насичення, представлений кількісний аналіз деформаційного зміцнення і динамічного знеміцнення, побудована триступенева визначає модель прогнозування напружень пластичної течії чистої міді. Як показує порівняння прогнозованого і виміряного напружень пластичної течії, за допомогою такої моделі можна точно описати гаряче деформування чистої міді при динамічному поверненні і / або рекристалізації. Виконано чисельне моделювання процесу висадки шляхом реалізації даної моделі в рамках комерційного програмного забезпечення. Модель вельми перспективна і може використовуватися для підвищення ефективності процесу гарячого кування деталей з чистої міді
CP violation in B→φKs in a model III two Higgs doublet model
The mixing induced time dependent CP asymmetry, direct CP asymmetry,
and branching ratio in B→φKs in a model III 2HDM are calculated,
in particular, neutral Higgs boson contributions are included. It is shown
that satisfying all the relevant experimental constraints, for time dependent
CP asymmetry SφK the model III can agree with the present data, Sφk =
−0.39±0.41, within the 1σ error, and the direct CP asymmetry which is zero
in SM can be about −8% ∼ −20% in the reasonable regions of parameters
Impaired heterologous immunity in aged ferrets during sequential influenza A H1N1 infection
The major burden of influenza morbidity resides within the elderly population. The challenge managing influenza-associated illness in the elderly is the decline of immune function, where mechanisms leading to immunological senescence have not been elucidated. To better represent the immune environment, we investigated clinical morbidity and immune function during sequential homologous and heterologous H1N1 influenza infection in an aged ferret model. Our findings demonstrated experimentally that aged ferrets had significant morbidity during monosubtypic heterologous 2° challenge with significant weight loss and respiratory symptoms. Furthermore, increased clinical morbidity was associated with slower and shorter hemagglutinin antibody generation and attenuated type 1 T-cell gene responses in peripheral blood. These results revealed dampened immune activation during sequential influenza infection in aged ferrets. With the presence of an aged model, dissecting clinical morbidity, viral dynamics and immune response during influenza infection will aid the development of future prophylactics such as age specific influenza vaccines
Compression Deformation Behavior and Processing Map of Pure Copper
To reveal compression deformation behavior of pure copper, the deformation characteristics of pure copper have been investigated by means of compression tests in the temperature range of 400–900°C and strain rate range of 0.001–1 s⁻¹. The results show that the flow stress of pure copper increases with increasing strain rate and decreasing deformation temperature, which is characterized by work-hardening, dynamic recovery, dynamic recrystallization, and secondary work-hardening, etc. The activation energy of hot deformation is associated with deformation temperature and strain rate, and the average activation energy is calculated to be 303.8 kJ/mol. The flow stress prediction model based on GA+BP possess, is in very good agreement with the true stress curve, which is of significance to the guidance of hot working of pure copper. The flow instability occurs in the intermediate strain rate region (0.01–0.1 s⁻¹) base on the analysis of processing map, the high power dissipation correspond to the dynamic recrystallization. Appropriate reducing the deformation temperature or increasing the strain rate is beneficial for the grain refinement in the steady-state region of the processing map
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