352 research outputs found
Polarisation of submillimetre lines from interstellar medium
Magnetic fields play important roles in many astrophysical processes.
However, there is no universal diagnostic for the magnetic fields in the
interstellar medium (ISM) and each magnetic tracer has its limitation. Any new
detection method is thus valuable. Theoretical studies have shown that
submillimetre fine-structure lines are polarised due to atomic alignment by
Ultraviolet (UV) photon-excitation, which opens up a new avenue to probe
interstellar magnetic fields. We will, for the first time, perform synthetic
observations on the simulated three-dimensional ISM to demonstrate the
measurability of the polarisation of submillimetre atomic lines. The maximum
polarisation for different absorption and emission lines expected from various
sources, including Star-Forming Regions (SFRs) are provided. Our results
demonstrate that the polarisation of submillimetre atomic lines is a powerful
magnetic tracer and add great value to the observational studies of the
submilimetre astronomy.Comment: 6 pages, 3 figures, MNRAS accepte
Understanding the multiwavelength observation of Geminga's TeV halo: the role of anisotropic diffusion of particles
In this letter we propose that the X-ray and the TeV observations in the
vicinity of Geminga can be understood in the framework of anisotropic diffusion
of injected electrons/positrons. This interpretation only requires the
turbulence in the vicinity of Geminga to be sub-Alfv\'enic with the local mean
magnetic field direction approximately aligned with our line of sight towards
Geminga, without invoking extreme conditions for the environment, such as an
extremely small diffusion coefficient and a weak magnetic field of strength
G as suggested in previous literature.Comment: 7 pages, 4 figures, including Supplemental Material, PRL accepte
Tracing Magnetic Fields by Atomic Alignment in Extended Radiation Fields
Tracing magnetic fields is crucial as magnetic fields play an important role
in many astrophysical processes. Earlier studies have demonstrated that Ground
State Alignment (GSA) is a unique way to detect weak magnetic fields (1G> B>
1exp(-15)G) in diffuse media, they consider the situation when the pumping
source is a point source, which applies when the star is very far away from the
diffuse media. In this paper, we explore the GSA in the presence of extended
radiation fields. For the radiation fields with a clear geometric structure, we
consider the alignment in circumstellar medium, binary systems, disc, and Local
Interstellar Medium (LISM). For the radiation fields with unidentified pumping
sources, we apply the method of multipole expansion and discuss the GSA induced
by each component. We demonstrate that for general radiation fields, it is
adequate to consider the contribution from dipole and quadrupole radiation
components. We find that in general polarization of absorption arizing from GSA
coincides with the projection of magnetic field in the 2D sky with 90 degree
degeneracy. We conclude that the GSA is a unique tool to detect the direction
of weak magnetic field, and it can be applied to diffuse media in any radiation
field.Comment: 17pages, 17 Figures, ApJ publishe
Identification of magnetosonic modes in Galactic turbulence with synchrotron polarization
The equipartition of magnetic and thermal energy in the interstellar medium
(ISM) indicates the magneto-hydrodynamic nature of the interstellar turbulence,
which can be decomposed into three wave modes: Alfv\'en, fast and slow
magnetosonic modes\cite{Herlofson50,LG01,CL03}. Even for studies performed in
the case of subsonic turbulence, the magnetosonic modes have been revealed to
be more effective than the Alfv\'enic modes for processes such as cosmic ray
(CR) transport and acceleration \cite{YL04,Lynn14}. The multiphase nature of
ISM and diversity of driving mechanisms give rise to spatial variation of
turbulence properties. Nevertheless, the employed model of magneto-hydrodynamic
turbulence is often oversimplified being assumed to be only Alfv\'enic or even
hydrodynamic due to a lack of observational evidence. Here we report the
employment of our novel method, the signature from polarization analysis (SPA),
on unveiling the plasma modes in interstellar turbulence. Its application leads
to the first discovery of magnetosonic modes in the Cygnus X region. It is
found that the magnetosonic modes overlap to a high degree with Fermi cocoon,
consistent with theoretical expectations. Moreover, through comparison with the
spectrum at other wavelengths, the plasma modes of turbulence are unveiled in
active star formation zones. The SPA casts light on the plasma modes
composition of the Galactic turbulence, and marks the onset of a new era in the
study of interstellar turbulence and accordingly our understandings of relevant
processes including cosmic ray transport and star formation
Cryopreservation of cell/hydrogel constructs based on a new cell-assembling technique
Organ manufacturing products hold the promise to be used widely in the future for complex organ failings. The cryopreservation of the product is a very important step in the commercialization activities. In this article, a new cell cryopreservation technique, whereby, cryoprotectants were directly incorporated into the cell/hydrogel constructs, prototyped according to the predesigned structure and then subjected to a special freezing/thawing process. The rheological and hydration properties of the cryopreservation systems indicated that the hydratabilities of the gelatin/alginate hydrogels were greatly increased while the eutectic temperatures were greatly decreased by the addition of glycerol. Dextran-40 was found to be effective to improve the cell survival when incorporated with glycerol. The optimal volume concentration of the cryopretectans was 2.5% (v/v) glycerol and 5% (g/mL) dextran-40 in the gelatin/alginate hydrogel. Under these conditions, the cell viability in the construct was 96.3 ± 3.4%. Microscopic, thiazolyl blue (MTT) and hematoxylin and eosin (HE) staining results all indicated that the cells began to proliferate after thawing. The cells in the gelatin/alginate hydrogel with both glycerol and dextran-40 had greater proliferations than with only glycerol or dextran-40. This approach holds promise for a variety of applications in cell assembly for high-throughput drug screening and complex organ manufacturing areas
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