Sinogram Affirmed Iterative Reconstruction (SAFIRE) versus weighted filtered back projection (WFBP) effects on quantitative measure in the COPDGene 2 test object

PURPOSE

Assessing pulmonary emphysema using Quantitative CT of the lung depends on accurate measures of CT density. Sinogram-Affirmed-Iterative-Reconstruction (SAFIRE) is a new approach for reconstructing CT data acquired at significantly lower doses. However, quantitative effects of this method remain unexplored. The authors investigated the effects on the median values of materials in the COPDGene2 test-object as a function of the reconstruction method [weighted filtered back projection (WFBP) versus SAFIRE], test-object size, dose, and material composition using a Siemens SOMATOM Definition FLASH CT scanner.

METHODS

The COPDGene2 test-object contains eight materials; acrylic, water, four foams (20 lb, 12 lb, lung-equivalent, and 4 lb emphysema-equivalent), internal and external-air. The test-object was scanned with three different outer ring sizes, simulating three different body habitus. There is an average size (36 cm) Ring A, large size (40 cm) Ring B, and small size Ring C (30 cm). The CT protocol used 120 kVp, 0.5 s rotation, 1.0 pitch, and a 0.6 slice collimation with progressively decreasing x-ray exposure values, 11.94-0.74 mGy. With a thorax length of 30 cm, the corresponding effective doses would be 5.01-0.31 mSv. The effects of using SAFIRE versus WFBP were assessed using a two tailed t-test for each ring size, material, and dose. Multivariable linear regression was used to evaluate the relative effects of ring size, material composition, dose, and reconstruction method on the measured median value in HU.

RESULTS

SAFIRE versus WFBP, at the largest ring size and two lowest doses there was a significant difference in median values of 4 lb-foam, p<0.01. Using the smallest ring size at the lowest dose level there was a significant difference in the median value of 4 lb-foam, but the effect size was small, 1 HU. There is a significant difference in median values of both internal and external air using both the small and medium size rings at the three lowest dose levels, p<0.05. There are significant differences noted at both high and low dose levels when using the large ring size in the median values of internal and external air when, p<0.05. These effects on 4 lb-foam, inside and outside air are shown to be in part due to truncation effects on the median value since the lowest HU value in the CT scale used is -1024 HU. Multivariable linear regression results demonstrated significant effects on the measured material median value and standard deviation due to ring size, material composition, dose level, and reconstruction method, p<0.05.

CONCLUSIONS

The authors have shown that there is no significant effect on the median values obtained when using WFBP versus SAFIRE in materials with CT density between 120 and -856 HU using three different test-object sizes and CT doses that vary from 11.94 to 0.74 mGy. The authors have demonstrated there are significant effects on median values obtained when using WFBP versus SAFIRE in materials with CT density values between -937 and -1000 HU depending on the ring size and dose used. As expected, there is considerable reduction in image noise (lower standard deviation) using SAFIRE versus WFBP with all ring sizes, doses, and materials in the COPDGene2 test-object.

Effects of van der Waals interaction and electric field on the electronic structure of bilayer MoS2

The modification of the electronic structure of bilayer MoS2 by an external electric field can have potential applications in optoelectronics and valleytronics. Nevertheless, the underlying physical mechanism is not clearly understood, especially the effects of the van der Waals interaction. In this study, the spin orbit-coupled electronic structure of bilayer MoS2 has been investigated using the first-principle density functional theory. We find that the van der Waals interaction as well as the interlayer distance has significant effects on the band structure. When the interlayer distance of bilayer MoS2 increases from 0.614 nm to 0.71 nm, the indirect gap between the Γ and Λ points increases from 1.25 eV to 1.70 eV. Meanwhile, the energy gap of bilayer MoS2 transforms from an indirect one to a direct one. An external electric field can shift down (up) the energy bands of the bottom (top) MoS2 layer and also breaks the inversion symmetry of bilayer MoS2. As a result, the electric field can affect the band gaps, the spin-orbit interaction and splits the valance bands into two groups. The present study can help us understand more about the electronic structures of MoS2 materials for potential applications in electronics and optoelectronics.

Abstract 1928: Reporter construct for functional and real-time evaluation of cytokeratin 14+ bladder cancer stem cells

Bladder cancer is the fifth most common malignancy in the US. We recently reported that bladder cancer stem cells isolated by cell surface markers (i.e. CD44/CD90/CD49f) express a higher level of the intermediate filament cytokeratin 14 (CK14). Importantly, patients with a higher fraction of CK14+ cancer cells correlated with worse survival outcomes. Therefore, this CK14+ cancer cell subpopulation warrants further functional evaluation and characterization.

In the current study, we report the generation and characterization of a lentiviral reporter construct that carries the gene promoter region of human KRT14 gene upstream to a red fluorescent protein (tdTomato; Tm). With this reporter stably integrated into the genome of bladder cancer cells, the viable CK14+ cancer cell subpopulation could be isolated by FACS and visualized by fluorescent microscopy. We first validated the reporter by demonstrating that Tm+ cancer cells indeed express a higher level of KRT14 mRNA and relatively lower levels of differentiated cell markers (i.e. KRT18 and UPK1B) by qPCR. Next, we verified both in vitro and in vivo that CK14+/Tm+ cancer cells have functional properties of cancer stem cells by demonstrating their enriched sphere-forming ability and proficient engraftment as xenograft tumors in immunocompromised mice. Since neoadjuvant chemotherapy is a well-established treatment approach in patients with high-risk bladder cancer, we investigated CK14+ and CK14- cancer cells' response to the cytotoxic chemotherapy, gemcitabine/cisplatin (GC). FACS-purified CK14+/Tm+ cancer cells were more resistant to GC chemotherapy in vitro than CK14-/Tm- cancer cells. These findings were confirmed with in vivo studies using both patient-derived xenografts and immortalized bladder cancer xenografts. GC treated xenografts demonstrated a greater expansion of CK14+ cancer cells than vehicle treated controls. Additionally, we obtained a panel of human bladder cancer specimens from patients before and after neoadjuvant GC chemotherapy (n=15) and evaluated the CK14 status. An expansion or persistence of an infiltrating pattern of CK14 in post-neoadjuvant GC chemotherapy tumor specimens was associated with worse overall survival.

Collectively, these findings verified the unique intrinsic biological properties of CK14+/Tm+ bladder cancer cells and their response to GC chemotherapy. Ongoing experiments using fluorescence live imaging will evaluate Tm+/- bladder cancer cells' response to chemotherapy. The capacity to observe this CK14+/Tm+ subpopulation and their trace response to cytotoxic chemotherapy in these studies will open up new avenues to study the mechanisms of chemoresistance.

Citation Format: Philip L. Ho, Antonina Kurtova, Jing Xiao, Ross Krasnow, Erica Lay, Senthil Pazhanisamy, Seth P. Lerner, Keith S. Chan. Reporter construct for functional and real-time evaluation of cytokeratin 14+ bladder cancer stem cells. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1928. doi:10.1158/1538-7445.AM2014-1928

Abstract 4801: Stromal-mediated collagen I signal in promoting bladder cancer progression

Bladder cancer is the fifth most common malignancy, which is mostly incurable as invasive disease. It is clinically important to study the mechanisms underlying bladder cancer progression. While the tumor microenvironment is widely established to play an active role in epithelial cancers, its contribution to bladder cancer remains unexplored. The presence of cancer-associated fibroblasts (CAFs), characterized by the co-expression of vimentin, alpha-smooth muscle actin, and tenascin C, has been associated with invasive bladder cancer. Nevertheless, functional contributions of CAFs to bladder cancer progression have not been studied.

Here,we report the successful isolation and molecular characterization of bladder CAFs. We further investigate their functional roles on bladder cancer progression, with an emphasis on stromal secreted collagen I in the paracrine activation of discoidin domain receptor (DDR1) signaling in neighboring bladder cancer cells.

Using bioinformatics analysis we found that invasive bladder cancer patients with elevated expression of CAF genes have a poorer survival than those with lower CAF gene expression. Subsequently, we isolated and characterized CAFs from patient-derived tissues. Co-transplantation of CAFs and bladder cancer cells as xenograft tumors revealed high collagen I (COL1) deposition in these tumors formed, while molecular analyses uncovered CAFs as the primary source of COL1. Further experiments verified that COL1 as a single extracellular matrix component could phenocopy the tumor phenotype resembling those co-transplanted with CAFs and cancer cells. Further, pre-stimulation with COL1 could also enhance metastatic colonization of bladder cancer cells to lung. Molecular analysis of these COL1 stimulated cancer cells revealed up-regulation of the collagen receptor DDR1, but not integrins. Immunohistochemical analysis confirmed the presence of DDR1+ cancer cells adjacent to CAFs in the primary tumor site, with enhanced and exclusive expression of DDR1 in paired lung metastasis. Oncomine analysis showed that invasive bladder cancer expressed higher mRNA levels of COL1 and DDRs than non-invasive cancer, indicating that collagen I-DDR1 interaction may be a generalized phenomenon during invasive bladder cancer progression. To delineate the molecular mechanism downstream to collagen I-DDR1 we studied the interaction of DDR1 and STAT3, a factor we previously reported to drive invasive bladder cancer progression. Stimulation of bladder cancer cells with COL1 revealed a time kinetic increase in total and activated DDR1 protein associated with STAT3 phosphorylation. Further analysis of lung metastasis confirmed the co-localization of DDR1 and nuclear active STAT3. Collectively, these findings uncovered a role of CAFs in bladder cancer progression via stromal mediated collagen I signaling and warrant further analysis of therapeutic options to target signaling components downstream to collagen I.

Citation Format: Antonina V. Kurtova, Jing Xiao, Erica J. Lay, Qianxing Mo, Seth P. Lerner, David R. Rowley, Keith S. Chan. Stromal-mediated collagen I signal in promoting bladder cancer progression. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4801. doi:10.1158/1538-7445.AM2014-4801

Anomalous quantized conductance in a half-metal/topological superconductor/half-metal junction

The composite topological superconductor (TS), which is made of one-dimensional spin-orbit coupled nanowire with proximity-induced superconductivity from an s-wave superconductor, is not a pure p-wave superconductor, but has a suppressed s-wave pairing. We calculate the conductance spectrum of a half-metal/TS/half-metal junction in order to probe the pairing states and the spin texture of the p-wave pairing. It is found that, besides the regular quantized conductance peak contributed by Majorana fermions (MFs) when the half-metal magnetization is parallel to the MF spin, an anomalous quantized conductance peak exists when they are almost antiparallel. The physical origin is the MF-assisted local Andreev reflection to condense s-wave pairings. The anomalous quantized conductance is also confirmed by the Kitaev's p-wave model with a nonzero s-wave pairing. The findings might provide a new way to find the MF.

The effect of interlayer coupling on electron transport in graphene nanoribbons: a potential method for nanoposition sensing

We report a study on the effect of electron transport in a monolayer armchair graphene nanoribbon due to coupling to another monolayer armchair graphene ribbon, which is put on top of the first one. The conductance of the bottom ribbon oscillates when the top ribbon moves, and the oscillation can be used to determine stepwise position changes of the top ribbon for step sizes as small as 3.68 Å. The conductance oscillation arises from the rapid electron probability oscillations in the lowest three subbands of an armchair graphene ribbon. The phenomenon has potential applications in nanoposition sensing.

Adsorbate electric fields on a cryogenic atom chip

We investigate the behavior of electric fields originating from adsorbates deposited on a cryogenic atom chip as it is cooled from room temperature to cryogenic temperature. Using Rydberg electromagnetically induced transparency, we measure the field strength versus distance from a 1 mm square of yttrium barium copper oxide (YBCO) patterned onto a yttria stabilized zirconia chip substrate. We find a localized and stable dipole field at room temperature and attribute it to a saturated layer of chemically adsorbed rubidium atoms on the YBCO. As the chip is cooled towards 83 K we observe a change in sign of the electric field as well as a transition from a localized to a delocalized dipole density. We relate these changes to the onset of physisorption on the chip surface when the van der Waals attraction overcomes the thermal desorption mechanisms. Our findings suggest that through careful selection of substrate materials, it may be possible to reduce the electric fields caused by atomic adsorption on chips, opening up experiments to controlled Rydberg-surface coupling schemes.

Disorder effect on the integer quantum Hall effect in trilayer graphene

We numerically investigate the disorder effect on the integer quantum Hall effect in a trilayer graphene (TLG) system by use of the Kubo formula. For a clean sample, both Bernal (ABA) and rhombohedral (ABC) stacked TLGs display the same quantum rule with abnormal quantized Hall plateaus σxy = νe(2)/h (ν =± 6, ± 10, ± 14,…) in the band center and normal quantized Hall plateaus at the band edges. In the presence of disorder, the Hall plateaus become obscure and the higher plateaus disappear first with the increase of the disorder; however, the Hall plateaus of the ABA-stacked TLG are destroyed more readily in comparison with the ABC-stacked one. The longitudinal conductance minimums of the system corresponding to the Hall plateaus become narrower and thinner with disorder, and those of the ABC-stacked TLG are comparatively more stable than those of the ABA structure. The findings indicate that the l = 3 chiral quasiparticles with cubic energy dispersion in ABC-stacked TLG have comparatively stronger immunity to the disorder than the l = 1 and 2 chiral quasiparticles in the ABA counterpart.

Surface roughness induced electron mobility degradation in InAs nanowires

In this work, we present a study of the surface roughness dependent electron mobility in InAs nanowires grown by the nickel-catalyzed chemical vapor deposition method. These nanowires have good crystallinity, well-controlled surface morphology without any surface coating or tapering and an excellent peak field-effect mobility up to 15,000 cm(2) V(-1) s(-1) when configured into back-gated field-effect nanowire transistors. Detailed electrical characterizations reveal that the electron mobility degrades monotonically with increasing surface roughness and diameter scaling, while low-temperature measurements further decouple the effects of surface/interface traps and phonon scattering, highlighting the dominant impact of surface roughness scattering on the electron mobility for miniaturized and surface disordered nanowires. All these factors suggest that careful consideration of nanowire geometries and surface condition is required for designing devices with optimal performance.

The preclinical anti-angiogenic and pro-apoptotic activity of lenalidomide in urothelial carcinoma (UC)

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Background: Lenalidomide (Len) is an immunomodulatory drug (IMiD) approved for hematologic conditions and demonstrates immune modulation, anti-angiogenic activity and direct anti-tumor cytotoxicity. A rationale can be made to evaluate the preclinical activity of Len in UC. Methods: The in vitro anti-tumor activity of Len was evaluated in 4 human (5637, TCC-SUP, RT4, RT112) and 1 murine (MB49) cell line. Anti-proliferative activity activity (MTT assay), apoptosis (Annexin-FITC immunohistochemistry [IHC], flow cytometry) and cell viability by colony forming assay were measured. In vivo activity of daily oral Len 10 mg/kg or placebo orally for 5 days a week for up to 4 weeks was examined in syngeneic immunocompetent C57BL/6 mice bearing subcutaneous (SC) MB49-Luc25 tumors and RT4 subcutaneous xenografts. Tumors underwent immunohistochemistry (IHC) for microvessel density (CD31), apoptosis (cleaved caspase [cc]-3) and CD3+/CD20+ lymphocyte infiltration. Cereblon, a molecular target of Len was analyzed by IHC. Results: In vitro cultures for 3 days with daily repletion of Len showed significant pro-apoptotic activity (flow cytometry) at low micromolar concentrations attainable in human subjects (2.2 µM) against RT4 cells, a superficially invasive human UC cell line. Long-term cultures of RT4 cells for 2 weeks with daily repletion of Len significantly reduced cell viability and colony forming ability. Cereblon expression was numerically lower in sensitive RT4 cells compared to resistant 5637 cells (p=NS). In the immunocompetent model in vivo, Len did not decrease tumor size, or increase cc-3 and CD3+/CD20+ lymphocytes, but post-Len tumors exhibited decreased CD31 (p<0.05). In RT4 xenografts, Len significantly decreased the size of tumors and CD31, and increased cc-3 (all p<0.05). Cereblon expression increased in Len treated RT4 xenografts (p=0.024). Conclusions: Lenalidomide demonstrated selective preclinical activity against superficially invasive low grade human UC cells attributable to direct tumor cell apoptosis and anti-angiogenic activity. Clinical evaluation in patients with low grade or non-invasive UC and further study of cereblon as a predictive biomarker may be warranted.

Reference standard and statistical model for intersite and temporal comparisons of CT attenuation in a multicenter quantitative lung study

PURPOSE

The purpose of this study was to detect and analyze anomalies between a large number of computed tomography (CT) scanners, tracked over time, utilized to collect human pulmonary CT data for a national multicenter study: chronic obstructive pulmonary disease genetic epidemiology study (COPDGene).

METHODS

A custom designed CT reference standard "Test Object" has been developed to evaluate the relevant differences in CT attenuation between CT scanners in COPDGene. The materials used in the Test Object to assess CT scanner accuracy and precision included lung equivalent foam (-856 HU), internal air (-1000 HU), water (0 HU), and acrylic (120 HU). Nineteen examples of the Test Object were manufactured. Initially, all Test Objects were scanned on the same CT scanner before the Test Objects were sent to the 20 specific sites and 42 individual CT scanners that were used in the study. The Test Objects were scanned over 17 months while the COPDGene study continued to recruit subjects. A mixed linear effect statistical analysis of the CT scans on the 19 Test Objects was performed. The statistical model reflected influence of reconstruction kernels, tube current, individual Test Objects, CT scanner models, and temporal consistency on CT attenuation.

RESULTS

Depending on the Test Object material, there were significant differences between reconstruction kernels, tube current, individual Test Objects, CT scanner models, and temporal consistency. The two Test Object materials of most interest were lung equivalent foam and internal air. With lung equivalent foam, there were significant (p < 0.05) differences between the Siemens B31 (-856.6, ±0.82; mean ± SE) and the GE Standard (-856.6 ± 0.83) reconstruction kernel relative to the Siemens B35 reference standard (-852.5 ± 1.4). Comparing lung equivalent foam attenuation there were also significant differences between CT scanner models (p < 0.01), tube current (p < 0.005), and in temporal consistency (p < 0.005) at individual sites. However, there were no significant effects measurable using different examples of the Test Objects at the various sites compared to the reference scans of the 19 Test Objects. For internal air, significant (p < 0.005) differences were found between all reconstruction kernels (Siemens B31, GE Standard, and Phillips B) compared to the reference standard. There were significant differences between CT models (p < 0.005), and tube current (p < 0.005). There were no significant effects measurable using different examples of the Test Objects at the various sites compared to the reference scans of the 19 Test Objects. Differences, across scanners, between external air and internal air measures in this simple (relative to the in vivo lung) test object varied by as much as 15 HU.

CONCLUSIONS

The authors conclude that the Test Object designed for this study was able to detect significant effects regarding individual CT scanners that altered the CT attenuation measurements relevant to the study that are used to determine lung density. Through an understanding of individual scanners, the Test Object analysis can be used to detect anomalies in an individual CT scanner and to statistically model out scanner differences and individual scanner changes over time in a large multicenter trial.

The preclinical activity of lenalidomide in urothelial carcinoma (UC)

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Background: Lenalidomide is approved for multiple myeloma and deletion 5q myelodysplastic syndromes (MDS) and demonstrates immune modulation, anti-angiogenic activity and direct anti-tumor cytotoxicity. A rationale can be made to evaluate the preclinical activity of lenalidomide in urothelial carcinoma (UC) based on the importance of these pathways. Methods: The in vitro anti-tumor activity of lenalidomide was evaluated in 4 human (5637, TCC-SUP, RT4, RT112) and 1 murine (MB49) cell line. Anti-proliferative activity activity (MTT assay), apoptosis (Annexin-FITC immunohistochemistry [IHC], flow cytometry) and cell viability by colony forming assay were measured. In vivo examination of activity of daily oral lenalidomide 10 mg/kg orally once daily or placebo for 4 weeks is examined in a syngeneic immunocompetent mouse model employing MB49-Luc25 cells injected subcutaneously in C57BL/6 mice. Murine tumors will be studied for anti-tumor activity. Results: In vitro activity of lenalidomide was detected at low ~1 µM concentrations (attainable in human subjects) against a non-invasive human UC cell line (RT4). Long-term cultures of RT4 cells for 10 days with daily repletion of lenalidomide reduced cell viability and colony forming ability to 75.6% of controls. Induction of apoptosis in RT4 was demonstrated by Annexin-FITC IHC and flow cytometry compared to control (30.11 vs. 14.74%). Invasive human UC cells and murine MB49 cells did not demonstrate apoptosis with lenalidomide exposure in vitro. Futher, lenalidomide did not inhibit overall tumor growth in the syngeneic immunocompetent murine model; immune activity and stem cell directed activity will be presented. Conclusions: Lenalidomide demonstrated preclinical anti-tumor activity against non-invasive human UC cells. Given its favorable toxicity profile compared to cytotoxic chemotherapy, clinical evaluation in patients with non-muscle-invasive bladder cancer and recurrence after BCG therapy may be warranted.

A bipolar spin-filtering effect in graphene zigzag nanoribbons with spin-orbit coupling

We predict a large spin-filtering effect in graphene zigzag nanoribbons in the presence of Rashba spin-orbit coupling. The spin polarization of the transmitted current reaches a maximum when the incoming electrons occupy only one subband and the outgoing electrons occupy two subbands (spin is not taken into account). This situation can be reached by applying a potential barrier or a width constriction to the incoming lead of the ribbon. A simple physical picture is provided to explain the spin-filtering effect. Because of the electron-hole symmetry and the time-reversal symmetry, the spin-filtering is antisymmetric for the hole when compared with that for the electron. So the bipolar spin-polarized current can be generated by tuning the Fermi energy across the Dirac point. Besides, the wedge-shaped constriction can modify the conductance spin polarization.

Pure spin current generation in monolayer graphene by quantum pumping

We study a method to generate pure spin current in monolayer graphene over a wide range of Fermi energy by adiabatic quantum pumping. The device consists of three gate electrodes and two ferromagnetic strips, which induce a spin-splitting in the graphene through the proximity effect. A pure spin current is generated by applying two periodic oscillating gate voltages. We find that the pumped pure spin current is a sensitive oscillatory function of the Fermi energy. Large spin currents can be found at Fermi energies where there are Fabry-Perot resonances in the barriers. Furthermore, we analyze the effects of the parameters of the system on the pumped currents. Our predicted pumped spin current can be of the order of 100 nA which is measurable using the current technology. The proposed method is useful in the realization of graphene spintronic devices.

The dynamical conductance of graphene tunnelling structures

The dynamical conductances of graphene tunnelling structures were numerically calculated using the scattering matrix method with the interaction effect included in a phenomenological approach. The overall single-barrier dynamical conductance is capacitative. Transmission resonances in the single-barrier structure lead to dips in the capacitative imaginary part of the response. This is different from the ac responses of typical semiconductor nanostructures, where transmission resonances usually lead to inductive peaks. The features of the dips depend on the Fermi energy. When the Fermi energy is below half of the barrier height, the dips are sharper. When the Fermi energy is higher than half of the barrier height, the dips are broader. Inductive behaviours can be observed in a double-barrier structure due to the resonances formed by reflection between the two barriers.

Transverse spin current in the s-wave/p-wave Josephson junction

We report a theoretical study on spin transport in the hybrid Josephson junction composed of singlet s-wave and triplet p-wave superconductor. The node of the triplet pair potential is considered perpendicular to the interface of the junction. Based on a symmetry analysis, we predict that there is no net spin density at the interface of the junction but instead a transverse mode-resolved spin density can exist and a nonzero spin current can flow transversely along the interface of the junction. The predictions are numerically demonstrated by means of the lattice Matsubara Green's function method. It is also shown that, when a normal metal is sandwiched in between two superconductors, both spin current and transverse mode-resolved spin density are only residing at two interfaces due to the smearing effect of the multimode transport. Our findings are useful for identifying the pairing symmetry of the p-wave superconductor and generating spin current.

Spin-polarized quantum pumping in bilayer graphene

We study adiabatic quantum pumping in bilayer graphene where two-barrier potentials are weakly modulated as pumping parameters. Comparing the results with those for a normal quantum pump of non-chiral quasiparticles, we find that the chirality of quasiparticles in bilayer graphene heavily affects the pumped current through chiral tunnelling. When an exchange splitting induced by the proximity of a ferromagnetic insulator is introduced, the pumped current becomes spin-polarized. It is interesting that an almost 100% polarized charge current and a pure spin current with vanishing charge current can all be achieved under suitable conditions. The experimental feasibility and the interlayer asymmetric effect in bilayer graphene caused by the gate and the ferromagnet structures are also discussed. The results are useful for spintronics applications based on graphene.

Spin accumulation in triplet Josephson junction

We employ a Hamiltonian method to study the equal-spin pairing triplet Josephson junction with different orbital symmetries of pair potentials. Both the spin/charge supercurrent and possible spin accumulation at the interface of the junction are analyzed by means of the Keldysh Green's function. It is found that a spontaneous angle-resolved spin accumulation can form at the junction's interface when the orbital symmetries of Cooper pairs in two triplet superconductors are different, the physical origin is the combined effect of the different orbital symmetries and different spin states of Cooper pairs due to the misalignment of two d vectors in triplet leads. An abrupt current reversal effect induced by misalignment of d vectors is observed and can survive in a strong interface barrier scattering because the zero-energy state appears at the interface of the junction. These properties of the p-wave Josephson junction may be helpful for identifying the order parameter symmetry.

Spin current pumped by a rotating magnetic field in zigzag graphene nanoribbons

We study electron spin resonance in zigzag graphene nanoribbons by applying a rotating magnetic field on the system without any bias. By using the nonequilibrium Green's function technique, the spin-resolved pumped current is explicitly derived in a rotating reference frame. The pumped spin current density increases with the system size and the intensity of the transverse rotating magnetic field. For graphene nanoribbons with an even number of zigzag chains, there is a nonzero pumped charge current in addition to the pumped spin current owing to the broken spatial inversion symmetry of the system, but its magnitude is much smaller than the spin current. The short-ranged static disorder from either impurities or defects in the ribbon can depress the spin current greatly due to the localization effect, whereas the long-ranged disorder from charge impurities can avoid inter-valley scattering so that the spin current can survive in the strong disorder for the single-energy mode.

Spin reversal effect in hybrid s(±)-wave/p-wave Josephson junction

We report a theoretical study on a hybrid Josephson junction consisting of a proposed s( ± )-wave ferropnictide superconductor and a p-wave superconductor. It is found that the relative π phase shift intrinsic to the s( ± )-wave pairing can lead to an accumulated spin reversal effect at the junction interface and that the critical current has a vanishing point with the variation of the ratio of the interface resistances for each band. The spin reversal effect also appears with an increase of temperature and meanwhile the critical current exhibits a reentrant behavior. These findings can not appear for a usual s-wave state, so that they can be used to discriminate the s( ± )-wave pairing in superconducting ferropnictides from the conventional s-wave symmetry.

Triplet Josephson current modulated by Rashba spin-orbit coupling

We study the Rashba spin-orbit coupling (RSOC) effect on the supercurrent in a clean triplet superconductor/two-dimensional electron gas/triplet superconductor (TS/2DEG/TS) junction, where RSOC is considered in the 2DEG region. Based on the Bogoliubov-de Gennes equation and quantum scattering method, we show that RSOC can lead to a 0-π oscillation of supercurrent and the abrupt current reversal effect. The current direction can be reversed by a tiny modulation of RSOC, and this is attributed to the equal spin pairing of the TS order parameter and the spin precession phase of the quasiparticle traveling in the RSOC region. The RSOC strength can be controlled by an electric field in experiments, thus our findings provide a purely electric means to modulate the supercurrent in TS Josephson junctions.

Spin-polarized transport induced by spin-pumping in a Rashba ring

The Keldysh Green's function method is employed to study spin-dependent electron transport through a Rashba ring with a quantum dot (QD) embedded in one of its arms. Zero charge bias is applied on the system while a rotating magnetic field is considered in the QD to pump pure spin current. The Rashba spin-orbital coupling (RSOC) can cause a spin precession phase of the electron passing through the ring, so that the quantum interference in the ring can lead to a spin-polarized charge current flowing in the leads and the arm without a QD, whereas only pure spin current is flowing in the other arm with a QD. It is shown that for low frequency ω of the rotating magnetic field, the pumped charge current is proportional to ω unlike the charge current produced by mono-parametric quantum charge pumping, which is usually proportional to ω(2). Moreover, the magnitude, the direction, as well as the spin-polarization of the charge current can be controlled by tuning the device parameters such as the QD energy level, the RSOC strength, and the strength of the electron tunneling between the leads and the QD. Hence the studied device may serve as a generating source for tunable spin-polarized current in the spintronics field.