485 research outputs found
Magnetic Ordering in V-Layers of the Superconducting System of Sr2VFeAsO3
Results of transport, magnetic, thermal, and 75As-NMR measurements are
presented for superconducting Sr2VFeAsO3 with an alternating stack of FeAs and
perovskite-like block layers. Although apparent anomalies in magnetic and
thermal properties have been observed at ~150 K, no anomaly in transport
behaviors has been observed at around the same temperature. These results
indicate that V ions in the Sr2VO3-block layers have localized magnetic moments
and that V-electrons do not contribute to the Fermi surface. The electronic
characteristics of Sr2VFeAsO3 are considered to be common to those of other
superconducting systems with Fe-pnictogen layers.Comment: 4 pages, 4 figures, To appear in JPSJ 79 (2010) 12371
Study of Ni-doping Effect of Specific Heat and Transport Properties for LaFe1-yNiyAsO0.89F0.11
Specific heats and transport quantities of the LaFe1-yNiyAsO0.89F0.11 system
have been measured, and the results are discussed together with those reported
previously by our group mainly for LaFe1-yCoyAsO0.89F0.11 and
LaFeAsO0.89-xF0.11+x systems. The y dependence of the electronic specific heat
coefficient gamma can basically be understood by using the rigid-band picture,
where Ni ions provide 2 electrons to the host conduction bands and behave as
nonmagnetic impurities. The superconducting transition temperature Tc of
LaFe1-yNiyAsO0.89F0.11 becomes zero, as the carrier density p (=2y+0.11) doped
to LaFeAsO reaches its critical value p_c_ ~0.2. This p_c_ value of ~0.2 is
commonly observed for LaFe1-yCoyAsO0.89F0.11 and LaFeAsO0.89-xF0.11+x systems,
in which the relations p = x+0.11 and p = y+0.11 hold, respectively. As we
pointed out previously, the critical value corresponds to the disappearance of
the hole-Fermi surface. These results indicate that the carrier number solely
determines the Tc value. We have not observed appreciable effects of pair
breaking, which originates from the nonmagnetic impurity scattering of
conduction electrons and strongly suppresses T_c_ values of systems with
sign-reversing of the order parameter over the Fermi surface(s). On the basis
of the results, the so-called s_+-_ symmetry of the order parameter with the
sign-reversing is excluded.Comment: 4 pages, 7 figures, submitted to J. Phys. Soc. Jpn, (modified
version
Lasing oscillation in a three-dimensional photonic crystal nanocavity with a complete bandgap
We demonstrate lasing oscillation in a three-dimensional photonic crystal
nanocavity. The laser is realized by coupling a cavity mode, which is localized
in a complete photonic bandgap and exhibits the highest quality factor of
~38,500, with high-quality semiconductor quantum dots. We show a systematic
change in the laser characteristics, including the threshold and the
spontaneous emission coupling factor by controlling the crystal size, which
consequently changes the strength of photon confinement in the third dimension.
This opens up many interesting possibilities for realizing future ultimate
light sources and three-dimensional integrated photonic circuits and for more
fundamental studies of physics in the field of cavity quantum electrodynamics.Comment: 14 pages, 4 figure
CRAFTing Delivery of Membrane Proteins into Protocells using Nanodiscs
For the successfulgenerativeengineeringof functionalartificialcells,a convenientandcontrollablemeansof deliveringmembraneproteinsinto membranelipidbilayersis necessary.Herewereporta deliverysystemthatachievesthis by employingmembraneprotein-carryingnanodiscsandthecalcium-dependentfusionofphosphatidylserinelipidmembranes.We showthat lipidnanodiscscanfuse a transportedlipidbilayerwith the lipidbilayersof smallunilamellarvesicles(SUVs)or giantunilamellarvesicles(GUVs)whileavoidingrecipientvesiclesaggregation.Thisis triggeredby a simple,transientincreasein calciumconcentration,whichresultsin efficientand rapidfusionin a one-potreaction.Furthermore,nanodiscscan be loadedwithmembraneproteinsthatcan be deliveredintotargetSUVor GUVmembranesin a detergent-independentfashionwhileretainingtheirfunctionality.Nanodiscshavea provenabilityto carrya widerangeof membraneproteins,controltheiroligomericstate,and arehighlyadaptable.Giventhis, our approachmay be the basisfor the developmentof usefultoolsthat will allowbespokedeliveryofmembraneproteinsto protocells,equippingthemwith the cell-likeabilityto exchangematerialacrossouter/subcellularmembranes
A Whole-Chromosome Analysis of Meiotic Recombination in Drosophila melanogaster
Although traditional genetic assays have characterized the pattern of crossing over across the genome in Drosophila melanogaster, these assays could not precisely define the location of crossovers. Even less is known about the frequency and distribution of noncrossover gene conversion events. To assess the specific number and positions of both meiotic gene conversion and crossover events, we sequenced the genomes of male progeny from females heterozygous for 93,538 X chromosomal single-nucleotide and InDel polymorphisms. From the analysis of the 30 F1 hemizygous X chromosomes, we detected 15 crossover and 5 noncrossover gene conversion events. Taking into account the nonuniform distribution of polymorphism along the chromosome arm, we estimate that most oocytes experience 1 crossover event and 1.6 gene conversion events per X chromosome pair per meiosis. An extrapolation to the entire genome would predict approximately 5 crossover events and 8.6 conversion events per meiosis. Mean gene conversion tract lengths were estimated to be 476 base pairs, yielding a per nucleotide conversion rate of 0.86 × 10−5 per meiosis. Both of these values are consistent with estimates of conversion frequency and tract length obtained from studies of rosy, the only gene for which gene conversion has been studied extensively in Drosophila. Motif-enrichment analysis revealed a GTGGAAA motif that was enriched near crossovers but not near gene conversions. The low-complexity and frequent occurrence of this motif may in part explain why, in contrast to mammalian systems, no meiotic crossover hotspots have been found in Drosophila
Feedback between p21 and reactive oxygen production is necessary for cell senescence
The sustained activation of CDKN1A (p21/Waf1/Cip1) by a DNA damage response induces mitochondrial dysfunction and reactive oxygen species (ROS) production via signalling through CDKN1A-GADD45A-MAPK14- GRB2-TGFBR2-TGFbeta in senescing primary human and mouse cells in vitro and in vivo.Enhanced ROS production in senescing cells generates additional DNA damage. Although this damage is repairable and transient, it elevates the average levels of DNA damage response permanently, thus forming a positive feedback loop.This loop is necessary and sufficient to maintain the stability of growth arrest until a ‘point of no return' is reached during establishment of senescence
Preclinical evaluation of the efficacy of an antibody to human SIRPα for cancer immunotherapy in humanized mouse models
Tumor-associated macrophages (TAMs) are abundant in the tumor microenvironment and are considered potential targets for cancer immunotherapy. To examine the antitumor effects of agents targeting human TAMs in vivo, we here established preclinical tumor xenograft models based on immunodeficient mice that express multiple human cytokines and have been reconstituted with a human immune system by transplantation of human CD34 hematopoietic stem and progenitor cells (HIS-MITRG mice). HIS-MITRG mice supported the growth of both human cell line (Raji)- and patient-derived B cell lymphoma as well as the infiltration of human macrophages into their tumors. We examined the potential antitumor action of an antibody to human SIRPα (SE12C3) that inhibits the interaction of CD47 on tumor cells with SIRPα on human macrophages and thereby promotes Fcγ receptor-mediated phagocytosis of the former cells by the latter. Treatment with the combination of rituximab (antibody to human CD20) and SE12C3 inhibited Raji tumor growth in HIS-MITRG mice to a markedly greater extent than did rituximab monotherapy. This enhanced antitumor effect was dependent on human macrophages and attributable to enhanced rituximab-dependent phagocytosis of lymphoma cells by human macrophages. Treatment with rituximab and SE12C3 also induced reprogramming of human TAMs toward a proinflammatory phenotype. Furthermore, the combination treatment essentially prevented the growth of patient-derived diffuse large B cell lymphoma in HIS-MITRG mice. Our findings thus support the study of HIS-MITRG mice as a model for the preclinical evaluation in vivo of potential therapeutics, such as antibodies to human SIRPα, that target human TAMs
- …