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 $<1\mu$G as suggested in previous literature.Comment: 7 pages, 4 figures, including Supplemental Material, PRL accepte

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

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

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 &#xb1; 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