639 research outputs found
Reverse Doppler Effect of Sound
We report observation of reverse Doppler effect in a double negative acoustic
metamaterial. The metamaterial exhibited negative phase velocity and positive
group velocity. The dispersion relation is such that the wavelength
corresponding to higher frequency is longer. We observed that the frequency was
down-shifted for the approaching source, and up-shifted when the source
receded
Shear Current Effects on Monochromatic Water Waves Crossing Trenches
The reflection coefficients of monochromatic water waves over trenches with shear current are estimated analytically. The diffraction of waves by an abrupt depth change and shear current is formulated by the matched eigenfunction expansion method. The proper number of steps and evanescent modes are proposed by a series of convergence tests. The accuracy of the predicted reflection coefficients is checked by estimating the wave energy. Reflection and transmission characteristics are studied for various shear current conditions. The different combinations of strength, width of shear current, and incident wave angle with constant water depth topography are examined. The optimal figure of the trench with shear current is obtained by estimating the reflection coefficients for various sloped transitions. The resonant reflection of the water waves is found by multiarrayed optimal trenches and the interaction of sinusoidally varying topography with shear current
High-resolution near-IR Spectral mapping with H and [Fe II] lines of Multiple Outflows around LkH 234
We present a high-resolution, near-IR spectroscopic study of multiple
outflows in the LkH 234 star formation region using the Immersion
GRating INfrared Spectrometer (IGRINS). Spectral mapping over the blueshifted
emission of HH 167 allowed us to distinguish at least three separate, spatially
overlapped, outflows in H and [Fe II] emission. We show that the H
emission represents not a single jet, but complex multiple outflows driven by
three known embedded sources: MM1, VLA 2, and VLA 3. There is a redshifted
H outflow at a low velocity, \VLSR 50 {\kms}, with respect to
the systemic velocity of \VLSR 11.5 {\kms}, that coincides with the
HO masers seen in earlier radio observations two arcseconds southwest of
VLA 2. We found that the previously detected [Fe II] jet with \VLSR
100 {\kms} driven by VLA 3B is also detected in H emission, and confirm
that this jet has a position angle about 240. Spectra of the
redshifted knots at 14\arcsec65\arcsec northeast of LkH 234 are
presented for the first time. These spectra also provide clues to the existence
of multiple outflows. We detected high-velocity (50120 {\kms}) H gas
in the multiple outflows around LkH 234. Since these gases move at
speeds well over the dissociation velocity ( 40 {\kms}), the emission must
originate from the jet itself rather than H gas in the ambient medium.
Also, position-velocity diagrams and excitation diagram indicate that emission
from knot C in HH 167 come from two different phenomena, shocks and
photodissociation.Comment: 32 pages, 12 figures, 2 tables, Accepted for publication in the
Astrophysical Journa
Enhanced Solubility of the Support in an FDM-Based 3D Printed Structure Using Hydrogen Peroxide under Ultrasonication
Fused deposition modeling (FDM), one of the archetypal 3D printing processes, typically requires support structures matched to printed model parts that principally have undercut or overhung features. Thus, the support removal is an essential postprocessing step after the FDM process. Here, we present an efficient and rapid method to remove the support part of an FDM-manufactured product using the phenomenon of oxidative degradation of hydrogen peroxide. This mechanism was significantly effective on polyvinyl alcohol (PVA), which has been widely used as a support material in the FDM process. Compared to water, hydrogen peroxide provided a two times faster dissolution rate of the PVA material. This could be increased another two times by applying ultrasonication to the solvent. In addition to the rapidness, we confirmed that amount of the support residues removed was enhanced, which was essentially caused by the surface roughness of the FDM-fabricated part. Furthermore, we demonstrated that there was no deterioration with respect to the mechanical properties or shape geometries of the obtained 3D printed parts. Taken together, these results are expected to help enhance the productivity of FDM by reducing the postprocessing time and to allow the removal of complicated and fine support structures, thereby improving the design capability of the FDM technique
CVD-grown monolayer MoS2 in bioabsorbable electronics and biosensors
Transient electronics entails the capability of electronic components to dissolve or reabsorb in a controlled manner when used in biomedical implants. Here, the authors perform a systematic study of the processes of hydrolysis, bioabsorption, cytotoxicity and immunological biocompatibility of monolayer MoS2
One-Stage Reconstruction for Midfacial Defect after Radical Tumor Resection
A serious midface defect involving resection of squamous cell carcinoma originating from the hard palate was treated by an unusual reconstructive strategy. After tumor resection, surgical reconstruction was accomplished in one stage using one free flap with one distant and local flap: a radial forearm flap to reconstruct the upper lip, a forehead flap to reconstruct the external nose, a cantilever calvarial bone graft to replace the nasal skeleton and a nasolabial flap and split thickness skin graft to cover the internal nasal lining. The rationale for this one-stage reconstruction and the problems associated with midfacial reconstruction after wide tumor excision are discussed
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