943 research outputs found
Non-Gaussianity and gravitational wave background in curvaton with a double well potential
We study the density perturbation by a curvaton with a double well potential
and estimate the nonlinear parameters for non-Gaussianity and the amplitude of
gravitational wave background generated during inflation. The predicted
nonlinear parameters strongly depend on the size of a curvaton self-coupling
constant as well as the reheating temperature after inflation for a given
initial amplitude of the curvaton. The difference from usual massive
self-interacting curvaton is also emphasized.Comment: 23 pages, 6 figure
Modulated reheating by curvaton
There might be a light scalar field during inflation which is not responsible
for the accelerating inflationary expansion. Then, its quantum fluctuation is
stretched during inflation. This scalar field could be a curvaton, if it decays
at a late time. In addition, if the inflaton decay rate depends on the light
scalar field expectation value by interactions between them, density
perturbations could be generated by the quantum fluctuation of the light field
when the inflaton decays. This is modulated reheating mechanism. We study
curvature perturbation in models where a light scalar field does not only play
a role of curvaton but also induce modulated reheating at the inflaton decay.
We calculate the non-linearity parameters as well as the scalar spectral index
and the tensor-to-scalar ratio. We find that there is a parameter region where
non-linearity parameters are also significantly enhanced by the cancellation
between the modulated effect and the curvaton contribution. For the simple
quadratic potential model of both inflaton and curvaton, both tensor-to-scalar
ratio and nonlinearity parameters could be simultaneously large.Comment: 26 pages, 22 figure
Can Standard Model Higgs Seed the Formation of Structures in Our Universe?
We study the Standard Model Higgs field as a source for the primordial
curvature perturbation, particularly in the curvaton and modulated reheating
scenario. We conclude that the Higgs cannot play as a curvaton due to the small
energy density when it decays, however the modulated reheating by Higgs can be
a viable scenario. In the latter case, the non-Gaussianity is inevitably
generated and strongly constrains the type of potential of inflaton field and
Higgs-dependent interaction term. For the quadratic potential of the inflaton
field with decay rate which non-linearly depends on the Higgs vacuum
expectation value, the contribution of Higgs field to the primordial curvature
perturbation must be less than 8%.Comment: 12 pages; version accepted for publication in Phys.Rev.
Experimental and numerical study of micro deep drawing
© 2015 Owned by the authors, published by EDP Sciences. Micro forming is a key technology for an industrial miniaturisation trend, and micro deep drawing (MDD) is a typical micro forming method. It has great advantages comparing to other micro manufacturing methods, such as net forming ability, mass production potential, high product quality and complex 3D metal products fabrication capacity. Meanwhile, it is facing difficulties, for example the so-called size effects, once scaled down to micro scale. To investigate and to solve the problems in MDD, a combined micro blanking-drawing machine is employed and an explicit-implicit micro deep drawing model with a voronoi blank model is developed. Through heat treatment different grain sizes can be obtained, which affect material's properties and, consequently, the drawing process parameters, as well as produced cups' quality. Further, a voronoi model can provide detailed material information in simulation, and numerical simulation results are in accordance with experimental results
Formability of micro sheet hydroforming of ultra-fine grained stainless steel
© 2014 The Authors. Published by Elsevier Ltd. The formability of ultra-fine grained stainless steel is investigated in micro hydromechanical deep drawing. The materials used are ultra-fine grained stainless steel and SUS304-H with thickness of 20 and 50 m. The micro cups are successfully fabricated for the ultra-fine grained stainless steel but it cannot be fabricated for SUS304-H with thickness of 20 m. The fracture type of ultra-fine grained stainless steel foil is the shortage of tensile strength at plain strain state and does not change with a decrease of the thickness. In contrast, the fracture type of SUS304-H foil changes to the bending deformation with decreasing the thickness due to its low ductility. The ultra-fine grained metal foil is required to obtain the high formability and fabricate the sharp micro cups
Two-photon Bio-imaging with a Mode-locked Semiconductor Laser
Abstract: We demonstrated two-photon imaging of biological tissues by employing a mode-locked semiconductor laser. Kilowatt-peak-power second-harmonic pulses were obtained from amplified 1.55-µm optical pulses, and were used for two-photon excitation. ©2006 Optical Society of America OCIS codes: (140.5960) Semiconductor lasers; (170.3880) Medical and biological imaging. 1
Auto-tracking camera for dry-box laparoscopic training
While laparoscopic surgery is less invasive than open surgery and is now common in various medical fields, laparoscopic surgery often requires more time for the operator to achieve mastery. Dry box training is one of the most important methods for developing laparoscopic skill. However, the camera is usually fixed to a particular point, which is different from practical surgery, during which the operational field is constantly adjusted by an assistant. Therefore, we introduced a camera for dry box training that can be moved by surgeons as desired by using computer vision. By detecting the ArUco marker, the camera attached onto the servomotor successfully tracked the forceps automatically. This system could easily be modified and become operable by a foot switch or voice, and collaborations between surgeons and medical engineers are expected
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