2,752 research outputs found
Suppression of long-wavelength CMB spectrum from the no-boundary initial condition
The lack of correlations at the long-wavelength scales of the cosmic
microwave background spectrum is a long-standing puzzle and it persists in the
latest Planck data. By considering the Hartle-Hawking no-boundary wave function
as the initial condition of the inflationary universe, we propose that the
power suppression can be the consequence of a massive inflaton, whose initial
vacuum is the Euclidean instanton in a compact manifold. We calculate the
primordial power spectrum of the perturbations, and find that as long as the
scalar field is moderately massive, the power spectrum is suppressed at the
long-wavelength scales.Comment: 9 pages, 7 figures; journal versio
Improving Axial Resolution of Optical Resolution Photoacoustic Microscopy with Advanced Frequency Domain Eigenspace Based Minimum Variance Beamforming Method
Optical resolution photoacoustic microscopy (OR-PAM) leverages optical
focusing and acoustic detection for microscopic optical absorption imaging.
Intrinsically it owns high optical lateral resolution and poor acoustic axial
resolution. Such anisometric resolution hinders good 3-D visualization; thus
2-D maximum amplitude projection images are commonly presented in the
literature. Since its axial resolution is limited by the bandwidth of acoustic
detectors, ultrahigh frequency, and wideband detectors with Wiener
deconvolution have been proposed to address this issue. Nonetheless, they also
introduce other issues such as severe high-frequency attenuation and limited
imaging depth. In this work, we view axial resolution improvement as an axial
signal reconstruction problem, and the axial resolution degradation is caused
by axial sidelobe interference. We propose an advanced frequency-domain
eigenspace-based minimum variance (F-EIBMV) beamforming technique to suppress
axial sidelobe interference and noises. This method can simultaneously enhance
the axial resolution and contrast of OR-PAM. For a 25-MHz OR-PAM system, the
full-width at half-maximum of an axial point spread function decreased
significantly from 69.3 m to 16.89 m, indicating a significant
improvement in axial resolution
Synthesis and crystal structure of the first 6a-thiathiophthen metal complex [Mo(CO)_5PPh_(2]2)(µ-C_5H_2S_3)
The first 6a-thiathiophthen metal complex was prepared by treating M(CO_)5[PPh_2CS_2CH_2C≡CH] with a catalytic amount of secondary amine or tertiary amine; the structure of the 6a-thiathiophthen molybdenum complex is confirmed by an X-ray diffraction analysis
- …