34 research outputs found
EFFECTIVE DOSE MEASUREMENT FOR CONE BEAM COMPUTED TOMOGRAPHY USING GLASS DOSIMETER
During image-guided radiation therapy, the patient is exposed to unwanted radiation from imaging devices built into the medical LINAC. In the present study, the effective dose delivered to a patient from a cone beam computed tomography (CBCT) machine was measured. Absorbed doses in specific organs listed in ICRP Publication 103 were measured with glass dosimeters calibrated with kilovolt (kV) X-rays using a whole body physical phantom for typical radiotherapy sites, including the head and neck, chest, and pelvis. The effective dose per scan for the head and neck, chest, and pelvis were 3.37±0.29, 7.36±0.33, and 4.09±0.29 mSv, respectively. The results highlight the importance of the compensation of treatment dose by managing imaging dose
Pilot KaVA monitoring on the M87 jet: confirming the inner jet structure and superluminal motions at sub-pc scales
We report the initial results of our high-cadence monitoring program on the
radio jet in the active galaxy M87, obtained by the KVN and VERA Array (KaVA)
at 22 GHz. This is a pilot study that preceded a larger KaVA-M87 monitoring
program, which is currently ongoing. The pilot monitoring was mostly performed
every two to three weeks from December 2013 to June 2014, at a recording rate
of 1 Gbps, obtaining the data for a total of 10 epochs. We successfully
obtained a sequence of good quality radio maps that revealed the rich structure
of this jet from <~1 mas to 20 mas, corresponding to physical scales
(projected) of ~0.1-2 pc (or ~140-2800 Schwarzschild radii). We detected
superluminal motions at these scales, together with a trend of gradual
acceleration. The first evidence for such fast motions and acceleration near
the jet base were obtained from recent VLBA studies at 43 GHz, and the fact
that very similar kinematics are seen at a different frequency and time with a
different instrument suggests these properties are fundamental characteristics
of this jet. This pilot program demonstrates that KaVA is a powerful VLBI array
for studying the detailed structural evolution of the M87 jet and also other
relativistic jets.Comment: 10 pages, 9 figures, accepted for publication in PAS
Precessing jet nozzle connecting to a spinning black hole in M87
The nearby radio galaxy M87 offers a unique opportunity to explore the
connections between the central supermassive black hole and relativistic jets.
Previous studies of the inner region of M87 revealed a wide opening angle for
the jet originating near the black hole. The Event Horizon Telescope resolved
the central radio source and found an asymmetric ring structure consistent with
expectations from General Relativity. With a baseline of 17 years of
observations, there was a shift in the jet's transverse position, possibly
arising from an eight to ten-year quasi-periodicity. However, the origin of
this sideways shift remains unclear. Here we report an analysis of radio
observations over 22 years that suggests a period of about 11 years in the
position angle variation of the jet. We infer that we are seeing a spinning
black hole that induces the Lense-Thirring precession of a misaligned accretion
disk. Similar jet precession may commonly occur in other active galactic nuclei
but has been challenging to detect owing to the small magnitude and long period
of the variation.Comment: 41 pages, 7 figures, 7 table
Influence of Collecting Substrates on the Characterization of Hygroscopic Properties of Inorganic Aerosol Particles
The
influence of six collecting substrates with different physical
properties on the hygroscopicity measurement of inorganic aerosol
particle surrogates and the potential applications of these substrates
were examined experimentally. Laboratory-generated single salt particles,
such as NaCl, KCl, and (NH<sub>4</sub>)<sub>2</sub>SO<sub>4</sub>,
1–5 μm in size, were deposited on transmission electron
microscopy grids (TEM grids), parafilm-M, Al foil, Ag foil, silicon
wafer, and cover glass. The particle hygroscopic properties were examined
by optical microscopy. Contact angle measurements showed that parafilm-M
is hydrophobic, and cover glass, silicon wafer, Al foil, and Ag foil
substrates are hydrophilic. The observed deliquescence relative humidity
(DRH) values for NaCl, KCl, and (NH<sub>4</sub>)<sub>2</sub>SO<sub>4</sub> on the TEM grids and parafilm-M substrates agreed well with
the literature values, whereas the DRHs obtained on the hydrophilic
substrates were consistently ∼1–2% lower, compared to
those on the hydrophobic substrates. The water layer adsorbed on the
salt crystals prior to deliquescence increases the Gibb’s free
energy of the salt crystal–substrate system compared to the
free energy of the salt droplet–substrate system, which in
turn reduces the DRHs. The hydrophilic nature of the substrate does
not affect the measured efflorescence RH (ERH) values. However, the
Cl<sup>–</sup> or SO<sub>4</sub><sup>2–</sup> ions in
aqueous salt droplets seem to have reacted with Ag foil to form AgCl
or Ag<sub>2</sub>SO<sub>4</sub>, respectively, which in turn acts
as seeds for the heterogeneous nucleation of the original salts, leading
to higher ERHs. The TEM grids were found to be most suitable for the
hygroscopic measurements of individual inorganic aerosol particles
by optical microscopy and when multiple analytical techniques, such
as scanning electron microscopy-energy dispersive X-ray spectroscopy,
TEM-EDX, and/or Raman microspectrometry, are applied to the same individual
particles
Investigation of the Chemical Mixing State of Individual Asian Dust Particles by the Combined Use of Electron Probe X-ray Microanalysis and Raman Microspectrometry
In this work, quantitative electron probe X-ray microanalysis
(EPMA)
and Raman microspectrometry (RMS) were applied in combination for
the first time to characterize the complex internal structure and
physicochemical properties of the same ensemble of Asian dust particles.
The analytical methodology to obtain the chemical composition, mixing
state, and spatial distribution of chemical species within single
particles through the combined use of the two techniques is described.
Asian dust aerosol particles collected in Incheon, Korea, during a
moderate dust storm event were examined to assess the applicability
of the methodology to resolve internal mixtures within single particles.
Among 92 individual analyzed particles, EPMA and RMS identified 53%
of the particles to be internally mixed with two or more chemical
species. Information on the spatial distribution of chemical compounds
within internally mixed individual particles can be useful for deciphering
the particle aging mechanisms and sources. This study demonstrates
that the characterization of individual particles, including chemical
speciation and mixing state analysis, can be performed more in detail
using EPMA and RMS in combination than with the two single-particle
techniques alone