23,840 research outputs found
Superconductivity induced by oxygen deficiency in Sr-doped LaOFeAs
We synthesized Sr-doped sample with single phase,
and systematically studied the effect of oxygen deficiency in the Sr-doped
LaOFeAs system. It is found that substitution of Sr for La indeed induces the
hole carrier evidenced by positive thermoelectric power (TEP), but no bulk
superconductivity is observed. The superconductivity can be realized by
annealing the as-grown sample in vacuum to produce the oxygen deficiency. With
increasing the oxygen deficiency, the superconducting transition temperature
() increases and maximum reaches about 26 K the same as that in
La(O,F)FeAs. TEP dramatically changes from positive to negative in the
nonsuperconducting as-grown sample to the superconducting samples with oxygen
deficiency. While is always negative for all samples (even for Sr-doped
as grown sample). It suggests that the is
still electron-type superconductor.Comment: 4 pages, 4 figure
Transport properties and superconductivity in (M=La and K) with double FeAs layers
We synthesized the samples (M=La and K) with
-type structure. These samples were systematically characterized by
resistivity, thermoelectic power (TEP) and Hall coefficient ().
shows an anomaly in resistivity at about 140 K. Substitution of La
for Ba leads to a shift of the anomaly to low temperature, but no
superconducting transition is observed. Potassium doping leads to suppression
of the anomaly in resistivity and induces superconductivity at 38 K as reported
by Rotter et al.\cite{rotter}. The Hall coefficient and TEP measurements
indicate that the TEP is negative for and La-doped ,
indicating n-type carrier; while potassium doping leads to change of the sign
in and TEP. It definitely indicates p-type carrier in superconducting
with double FeAs layers, being in contrast to the case of
with single FeAs layer. A similar superconductivity is also
observed in the sample with nominal composition .Comment: 4 pages, 4 figure
Delayed implantation of a peripheral nerve graft reduces motoneuron survival but does not affect regeneration following spinal root avulsion in adult rats
Adult spinal motoneurons can regenerate their axons into a peripheral nerve (PN) graft following root avulsion injury if the graft is implanted immediately after the lesion is induced. The present study was designed to determine how avulsed motoneurons respond to a PN graft if implantation takes place a few days to a few weeks later. Survival, regeneration, and gene expression changes of injured motoneurons after delayed PN graft implantation were studied. The survival rates of spinal motoneurons were 78%, 65%, 57%, or 53% if a PN graft was implanted immediately, 1, 2, or 3 weeks after root avulsion, respectively. Interestingly, most of the surviving motoneurons were able to regenerate their axons into the graft regardless of the delay. All regenerating motoneurons expressed p75, but not nNOS, while all motoneurons that failed to regenerate expressed nNOS, but not p75. p75 and nNOS may, therefore, be used as markers for success or failure to regenerate axons. In the group with immediate graft implantation, 85% of the surviving motoneurons extended axons into the PN graft, while in the groups in which implantation was delayed 1, 2, or 3 weeks, 84%, 82%, and 83% of the surviving motoneurons, respectively, were found to have regenerated into the grafts. These findings indicate that avulsed spinal motoneurons retain the ability to regenerate for at least 3 weeks, and perhaps for as long as they survive. Therefore, the delayed implantation of a PN graft after root avulsion may provide a continued conducive environment to support regeneration.published_or_final_versio
Stealth Polydopamine-Based Nanoparticles with Red Blood Cell Membrane for the Chemo-Photothermal Therapy of Cancer
Herein, we developed curcumin (Cur)-loaded porous poly(lactic-co-glycolic acid) (pPLGA) nanoparticles (NPs) by the nanoprecipitation method. Dopamine (DA) was then self-polymerized to form a polydopamine (PDA) layer on the surface of the NPs, yielding Cur@pPLGA/PDA NPs that are able to act as both chemotherapeutic and photothermal agents. These NPs were further camouflaged with the red blood cell membrane (RBCM) to construct RBCM-Cur@pPLGA/PDA NPs. The RBCM-pPLGA/PDA NPs were around 200 nm in size and demonstrated photothermal performance in the near-infrared (NIR) region, with a potent conversion efficiency (35.2%). The blank carrier has favorable cytocompatibility, but when drug loaded the NPs can efficiently induce the death of cancer cells (particularly when combined with NIR laser treatment). Cellular uptake results revealed greater in vitro uptake of RBCM-Cur@pPLGA/PDA NPs than bare Cur@pPLGA/PDA NPs in the case of cancer cells but reduced macrophage phagocytosis. In vivo studies in mice showed that the RBCM-Cur@pPLGA/PDA NPs exhibited prolonged blood circulation times and excellent photothermal properties, allowing tumor-specific chemo-photothermal therapy. The RBCM-Cur@pPLGA/PDA NP platform presents great potential for targeted synergistic cancer treatments
Thermodynamic properties of Ba1-xMxFe2As2 (M = La and K)
The specific heat of BaFeAs single crystal, electron-doped
BaLaFeAs and hole-doped BaKFeAs
polycrystals were measured. For undoped BaFeAs single crystal, a very
sharp specific heat peak was observed at 136 K. This is attributed to the
structural and antiferromagnetic transitions occurring at the same temperature.
of the electron-doped non-superconducting
BaLaFeAs also shows a small peak at 120 K, indicating a
similar but weaker structural/antiferromagnetic transition. For the hole-doped
superconducting BaKFeAs, a clear peak of was
observed at = 36 K, which is the highest peak seen at superconducting
transition for iron-based high- superconductors so far. The electronic
specific heat coefficient and Debye temperature of these
compounds were obtained from the low temperature data
Temperature oscillation of a dual compensation chamber loop heat pipe under acceleration conditions
Loop heat pipe has a wide application in the fields of airborne electronics cooling and thermal management. However, the pertinent temperature oscillation of the loop heat pipe could lead to adverse effects on the electronics. In the current study, an ammonia-stainless steel dual compensation chamber loop heat pipe was developed to experimentally investigate the temperature oscillation under different acceleration conditions. The impact of several control parameters such as different heat loads, loading modes, acceleration directions and magnitudes on the operational performance of the loop heat pipe was analyzed in a systematic manner. The heat load applied on the evaporator ranged from 25 W to 300 W. The acceleration magnitude varied from 1 g to 9 g and four different acceleration direction, i.e. configurations A, B, C and D, were taken into account. Two different loading modes were applied with different heat load and acceleration force. Experimental results show that (i) the loop temperature will change and oscillate as the acceleration force was applied under all test conditions. It can be easily found that the temperature oscillation occurred at both heat loads of 250 W and 300 W. (ii) for the case of the first loading mode, periodic temperature oscillation is observed on the liquid line, whereas for the second loading mode, periodic temperature oscillation can be easily appeared on the entire loop. (iii) the loop temperature under both configurations A and B with acceleration of 7 g does not oscillate at heat load of 150 W, 200 W and 250 W when the first loading mode is applied. Especially under configuration B, the acceleration could contribute to repress the temperature oscillation. Under the current heat loads for almost all cases, the temperature oscillation can be observed for configurations A, C and D with acceleration of 5 g. (iv) the amplitude of evaporator at heat load of 300 W under configuration C are 0.6 °C, 0.3 °C, 0.2 °C and 0.3 °C with acceleration of 3 g, 5 g, 7 g and 9 g. The corresponding period is 66 s, 36 s, 34 s and 36 s, respectively
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