Electron scattering by Friedel oscillations in carbon nanotubes

Multi-walled carbon nanotube networks were confirmed to exhibit a linear decrease in resistivity with increasing temperature from 100 to above 400 K.The linearity was explained using a defect scattering model that involved Friedel oscillations(that is,electron-electron interactions).The applicability of this model,which was originally proposed for graphene,to carbon nanotubes was assessed based on a comparison of various experimental data.Increases in the slopes of the resistivity-temperature plots following the introduction of defects,as well as an effect of charge concentration on the slope were key predictions of this model.The results obtained from few-walled carbon nanotube networks are also shown.In the literature,linear resistivity-temperature plots were obtained from other graphene derivatives,indicating that the linearity originates from the hexagonal symmetry of these materials.The present work also indicated a relationship between the appearance of linearity and negative magnetoresistance above 100 K.Based on a mechanism incorporating scattering in association with Friedel oscillations and conventional electron conduction models,the universality of resistivity-temperature plots obtained from carbon nanotube networks is introduced.

Interleukin-12 supports in vitro self-renewal of long-term hematopoietic stem cells

Hematopoietic stem cells(HSCs)self-renew or differentiate through division.Cytokines are essential for inducing HSC division,but the optimal cytokine combination to control self-renewal of HSC in vitro remains unclear.In this study,we compared the effects of interleukin-12(IL-12)and thrombopoietin(TPO)in combination with stem cell factor(SCF)on in vitro self-renewal of HSCs.Single-cell assays were used to overcome the heterogeneity issue of HSCs,and serum-free conditions were newly established to permit reproduction of data.In single-cell cultures,CD150^(+)CD48^(-)CD41^(-)CD34^(-)c-Kit^(+)Sca-1^(+)lineage^(-)SCs divided significantly more slowly in the presence of SCF+IL-12 compared with cells in the presence of SCF+TPO.Serial transplantation of cells from bulk and clonal cultures revealed that TPO was more effective than IL-12 at supporting in vitro self-renewal of short-term(<6 months)HSCs,resulting in a monophasic reconstitution wave formation,whereas IL-12 was more effective than TPO at supporting the in vitro selfrenewal of long-term(>6 months)HSCs,resulting in a biphasic reconstitution wave formation.The control of division rate in HSCs appeared to be crucial for preventing the loss of self-renewal potential from their in vitro culture.