376 research outputs found
Thermodynamics of the Mg-B system: Implications for the deposition of MgB2 thin films
We have studied thermodynamics of the Mg-B system with the modeling technique
CALPHAD using a computerized optimization procedure. Temperature-composition,
pressure-composition, and pressure-temperature phase diagrams under different
conditions are obtained. The results provide helpful insights into appropriate
processing conditions for thin films of the superconducting phase, MgB2,
including the identification of the pressure/temperature region for
adsorption-controlled growth. Due to the high volatility of Mg, MgB2 is
thermodynamically stable only under fairly high Mg overpressures for likely
growth temperatures. This constraint places severe temperature constraints on
deposition techniques employing high vacuum conditions
rac-2,2′-(Thiane-2,6-diyl)bis[1-(4-bromophenyl)ethanone]
In the title compound, C21H20Br2O2S, prepared by the reaction of 1,9-bis(4-bromophenyl)nona-2,7-diene-1,9-dione with sodium sulfide nonahydrate in acetonitrile, the six-membered thiopyran ring has a chair conformation while the H atoms ortho to the S atom adopt a cis configuration. The dihedral angle between the two benzene rings is 2.59 (8)°
Fully Band Resolved Scattering Rate in MgB2 Revealed by Nonlinear Hall Effect and Magnetoresistance Measurements
We have measured the normal state temperature dependence of the Hall effect
and magnetoresistance in epitaxial MgB2 thin films with variable disorders
characterized by the residual resistance ratio RRR ranging from 4.0 to 33.3. A
strong nonlinearity of the Hall effect and magnetoresistance have been found in
clean samples, and they decrease gradually with the increase of disorders or
temperature. By fitting the data to the theoretical model based on the
Boltzmann equation and ab initio calculations for a four-band system, for the
first time, we derived the scattering rates of these four bands at different
temperatures and magnitude of disorders. Our method provides a unique way to
derive these important parameters in multiband systems.Comment: 4 pages, 4 figure
Superconducting properties of nanocrystalline MgB thin films made by an in situ annealing process
We have studied the structural and superconducting properties of MgB thin
films made by pulsed laser deposition followed by in situ annealing. The
cross-sectional transmission electron microscopy reveals a nanocrystalline
mixture of textured MgO and MgB with very small grain sizes. A
zero-resistance transition temperature () of 34 K and a zero-field
critical current density () of A/cm were obtained.
The irreversibility field was 8 T at low temperatures, although severe
pinning instability was observed. These bulk-like superconducting properties
show that the in situ deposition process can be a viable candidate for MgB
Josephson junction technologies
Differential expression of sPLA2 following spinal cord injury and a functional role for sPLA2-IIA in mediating oligodendrocyte death
After the initial mechanical insult of spinal cord injury (SCI), secondary mediators propagate a massive loss of oligodendrocytes. We previously showed that following SCI both the total phospholipase activity and cytosolic PLA(2)-IV alpha protein expression increased. However, the expression of secreted isoforms of PLA(2) (sPLA(2)) and their possible roles in oligodendrocyte death following SCI remained unclear. Here we report that mRNAs extracted 15 min, 4 h, 1 day, or 1 month after cervical SCI show marked upregulation of sPLA(2)-IIA and IIE at 4 h after injury. In contrast, SCI induced down regulation of sPLA(2)-X, and no change in sPLA(2)-IB, IIC, V, and XIIA expression. At the lesion site, sPLA(2)-IIA and IIE expression were localized to oligodendrocytes. Recombinant human sPLA(2)-IIA (0.01, 0.1, or 2 microM) induced a dose-dependent cytotoxicity in differentiated adult oligodendrocyte precursor cells but not primary astrocytes or Schwann cells in vitro. Most importantly, pretreatment with S3319, a sPLA(2)-IIA inhibitor, before a 30 min H(2)O(2) injury (1 or 10 mM) significantly reduced oligodendrocyte cell death at 48 h. Similarly, pretreatment with S3319 before injury with IL-1 beta and TNFalpha prevented cell death and loss of oligodendrocyte processes at 72 h. Collectively, these findings suggest that sPLA(2)-IIA and IIE are increased following SCI, that increased sPLA(2)-IIA can be cytotoxic to oligodendrocytes, and that in vitro blockade of sPLA(2) can create sparing of oligodendrocytes in two distinct injury models. Therefore, sPLA(2)-IIA may be an important mediator of oligodendrocyte death and a novel target for therapeutic intervention following SCI
The Long-term Monitoring Results of Insight-HXMT in the First 4 Yr Galactic Plane Scanning Survey
The first X-ray source catalog of Insight-HXMT Galactic Plane (|b|<10deg)
Scanning Survey (GPSS) is presented based on the data accumulated from June
2017 to August 2021. The 4 yr limit sensitivities at main energy bands can
reach 8.2x10^(-12) erg/s/cm^2} (2-6 keV), 4.21x10^(-11) erg/s/cm^2 (7-40 keV)
and 2.78x10^(-11) erg/s/cm^2 (25-100 keV). More than 1300 sources have been
monitored at a wide band (1100\,keV), of which 223 sources have a
signal-to-noise ratio greater than 5. We combined the GPSS data of Insight-HXMT
and MAXI and found it is feasible to obtain more complete long-term light
curves from their scanning results. The flux variabilities at different energy
bands of the 223 bright sources are analyzed based on the excess variances. It
is found that the fluxes of X-ray binaries are more active than those of
supernova remnants and isolated pulsars. Different types of binaries, e.g.,
low-mass X-ray binaries (LMXBs), high-mass X-ray binaries (HMXBs), neutron star
binaries, and black hole binaries, also distinctively show different
regularities. In addition, the relations between the hardness ratio (HR) and
excess variances, and HR and source types are analyzed. It is obvious that the
HRs of HMXBs tend to be harder than those of LMXBs and HMXBs tend to be more
active than those of LMXBs.Comment: 43 pages, 26 figures, accepted for publication in ApJ
Quantum Griffiths singularity in three-dimensional superconductor to Anderson critical insulator transition
Disorder is ubiquitous in real materials and can have dramatic effects on
quantum phase transitions. Originating from the disorder enhanced quantum
fluctuation, quantum Griffiths singularity (QGS) has been revealed as a
universal phenomenon in quantum criticality of low-dimensional superconductors.
However, due to the weak fluctuation effect, QGS is very challenging to detect
experimentally in three-dimensional (3D) superconducting systems. Here we
report the discovery of QGS associated with the quantum phase transition from
3D superconductor to Anderson critical insulator in a spinel oxide MgTi2O4
(MTO). Under both perpendicular and parallel magnetic field, the dynamical
critical exponent diverges when approaching the quantum critical point,
demonstrating the existence of 3D QGS. Among 3D superconductors, MTO shows
relatively strong fluctuation effect featured as a wide superconducting
transition region. The enhanced fluctuation, which may arise from the mobility
edge of Anderson localization, finally leads to the occurrence of 3D quantum
phase transition and QGS. Our findings offer a new perspective to understand
quantum phase transitions in strongly disordered 3D systems
Musashi1 expression cells derived from mouse embryonic stem cells can be enriched in side population isolated by fluorescence activated cell sorter
<p>Abstract</p> <p>Background</p> <p>Purifying stem cells is an inevitable process for further investigation and cell-therapy. Sorting side population (SP) cells is generally regarded as an effective method to enrich for progenitor cells. This study was to explore whether sorting SP could enrich for the Musashi1 (Msi1) positive cells from Msi1 high expression cells (Msi1<sup>high </sup>cells) derived from mouse embryonic stem cells (ESCs) in vitro.</p> <p>Results</p> <p>In this study, Msi1<sup>high </sup>cell population derived from ESCs were stained by Hoechst 33342, and then the SP and non-SP (NSP) fractions were analyzed and sorted by fluorescence activated cell sorter. Subsequently, the expressions of Msi1 and other markers for neural and intestinal stem cells in SP and NSP were respectively detected. SP and NSP cells were hypodermically engrafted into the backs of NOD/SCID mice to form grafts. The developments of neural and intestinal epithelial cells in these grafts were investigated. SP fraction was identified and isolated from Msi1<sup>high </sup>cell population. The expression of Msi1 in SP fraction was significantly higher than that in NSP fraction and unsorted Msi1<sup>high </sup>cells (<it>P</it>< 0.05). Furthermore, the markers for neural cells and intestinal epithelial cells were more highly expressed in the grafts from SP fraction than those from NSP fraction (<it>P</it>< 0.05).</p> <p>Conclusions</p> <p>SP fraction, isolated from Msi1<sup>high </sup>cells, contains almost all the Msi1-positive cells and has the potential to differentiate into neural and intestinal epithelial cells in vivo. Sorting SP fraction could be a convenient and practical method to enrich for Msi1-positive cells from the differentiated cell population derived from ESCs.</p
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