9,545 research outputs found
Valosin-containing protein regulates the proteasome-mediated degradation of DNA-PKcs in glioma cells.
DNA-dependent protein kinase (DNA-PK) has an important role in the repair of DNA damage and regulates the radiation sensitivity of glioblastoma cells. The VCP (valosine-containing protein), a chaperone protein that regulates ubiquitin-dependent protein degradation, is phosphorylated by DNA-PK and recruited to DNA double-strand break sites to regulate DNA damage repair. However, it is not clear whether VCP is involved in DNA-PKcs (DNA-PK catalytic subunit) degradation or whether it regulates the radiosensitivity of glioblastoma. Our data demonstrated that DNA-PKcs was ubiquitinated and bound to VCP. VCP knockdown resulted in the accumulation of the DNA-PKcs protein in glioblastoma cells, and the proteasome inhibitor MG132 synergised this increase. As expected, this increase promoted the efficiency of DNA repair in several glioblastoma cell lines; in turn, this enhanced activity decreased the radiation sensitivity and prolonged the survival fraction of glioblastoma cells in vitro. Moreover, the VCP knockdown in glioblastoma cells reduced the survival time of the xenografted mice with radiation treatment relative to the control xenografted glioblastoma mice. In addition, the VCP protein was also downregulated in ~25% of GBM tissues from patients (WHO, grade IV astrocytoma), and the VCP protein level was correlated with patient survival (R(2)=0.5222, P<0.05). These findings demonstrated that VCP regulates DNA-PKcs degradation and increases the sensitivity of GBM cells to radiation
Tunneling Qubit Operation on a Protected Josephson Junction Array
We discuss a protected quantum computation process based on a hexagon
Josephson junction array. Qubits are encoded in the punctured array, which is
topologically protected. The degeneracy is related to the number of holes. The
topological degeneracy is lightly shifted by tuning the flux through specific
hexagons. We also show how to perform single qubit operation and basic quantum
gate operations in this system.Comment: 8 pages, 4 figures. The published version in Phys. Rev.,
A81(2010)01232
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Exposure to hazardous volatile organic compounds, PM 10 and CO while walking along streets in urban Guangzhou, China
Toxic air pollutants in street canyons are important issues concerning public health especially in some large Asian cities like Guangzhou. In 1998 <18% of Guangzhou citizens used public transportation modes, with a majority commuting on foot (42%) or by bicycle (22%). Of the pedestrians, 57% were either senior citizens or students. In the present study, we measured toxic air pollutants while walking along urban streets in Guangzhou to evaluate pedestrian exposure. Volatile organic compounds (VOCs) were collected with sorbent tubes, and PM 10 and CO were measured simultaneously with portable analyzers. Our results showed that pedestrian exposure to PM 10 (with an average of 303 μg m -3 for all samples) and some toxic VOCs (for example, benzene) was relatively high. Monocyclic aromatic hydrocarbons were found to be the most abundant VOCs, and 71% of the samples had benzene levels higher than 30 μg m -3. Benzene, PM 10 and CO in walk-only streets were significantly lower (p<0.05) than in traffic streets, and the differences in exposure levels between new urban streets and old urban streets were highly significant (p<0.01). Pedestrian exposure to toxic VOCs and PM 10 was higher than those reported in other public transportation modes (bus and subway). The good correlations between BTEX, PM 10 and CO in the streets indicated that automotive emission might be their major source. Our study also showed that the risk to pedestrians due to air pollution was misinterpreted by the reported air quality index based on measurement of SO 2, NO x and PM 10 in the government monitoring stations. An urban roadside monitoring station might be needed by air quality monitoring networks in large Asian cities like Guangzhou, in order to survey exposure to air toxics in urban roadside microenvironments. © 2004 Elsevier Ltd. All rights reserved
Manipulation of heat current by the interface between graphene and white graphene
We investigate the heat current flowing across the interface between graphene
and hexagonal boron nitride (so-called white graphene) using both molecular
dynamics simulation and nonequilibrium Green's function approaches. These two
distinct methods discover the same phenomena that the heat current is reduced
linearly with increasing interface length, and the zigzag interface causes
stronger reduction of heat current than the armchair interface. These phenomena
are interpreted by both the lattice dynamics analysis and the transmission
function explanation, which both reveal that the localized phonon modes at
interfaces are responsible for the heat management. The room temperature
interface thermal resistance is about mK/W in zigzag
interface and mK/W in armchair interface, which
directly results in stronger heat reduction in zigzag interface. Our
theoretical results provide a specific route for experimentalists to control
the heat transport in the graphene and hexagonal boron nitride compound through
shaping the interface between these two materials.Comment: accepted by EP
Dimensional crossover of thermal conductance in graphene nanoribbons: A first-principles approach
First-principles density-functional calculations are performed to investigate
the thermal transport properties in graphene nanoribbons (GNRs). The
dimensional crossover of thermal conductance from one to two dimensions (2D) is
clearly demonstrated with increasing ribbon width. The thermal conductance of
GNRs in a few nanometer width already exhibits an approximate low-temperature
dependence of , like that of 2D graphene sheet which is attributed to
the quadratic nature of dispersion relation for the out-of-plane acoustic
phonon modes. Using a zone-folding method, we heuristically derive the
dimensional crossover of thermal conductance with the increase of ribbon width.
Combining our calculations with the experimental phonon mean-free path, some
typical values of thermal conductivity at room temperature are estimated for
GNRs and for 2D graphene sheet, respectively. Our findings clarify the issue of
low-temperature dependence of thermal transport in GNRs and suggest a
calibration range of thermal conductivity for experimental measurements in
graphene-based materials.Comment: 18 pages, 4 figure
Optical generation of hybrid entangled state via entangling single-photon-added coherent state
We propose a feasible scheme to realize the optical entanglement of
single-photon-added coherent state (SPACS) and show that, besides the Sanders
entangled coherent state, the entangled SPACS also leads to new forms of hybrid
entanglement of quantum Fock state and classical coherent state. We probe the
essential difference of two types of hybrid entangled state (HES). This HES
provides a novel link between the discrete- and the continuous-variable
entanglement in a natural way.Comment: 6 pages, 2 figure
Thermal conduction of carbon nanotubes using molecular dynamics
The heat flux autocorrelation functions of carbon nanotubes (CNTs) with
different radius and lengths is calculated using equilibrium molecular
dynamics. The thermal conductance of CNTs is also calculated using the
Green-Kubo relation from the linear response theory. By pointing out the
ambiguity in the cross section definition of single wall CNTs, we use the
thermal conductance instead of conductivity in calculations and discussions. We
find that the thermal conductance of CNTs diverges with the CNT length. After
the analysis of vibrational density of states, it can be concluded that more
low frequency vibration modes exist in longer CNTs, and they effectively
contribute to the divergence of thermal conductance.Comment: 15 pages, 6 figures, submitted to Physical Review
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Visualization of facet-dependent pseudo-photocatalytic behavior of TiO2 nanorods for water splitting using In situ liquid cell TEM
We report an investigation of the pseudo-photocatalytic behavior of rutile TiO2 nanorods for water splitting observed with liquid cell transmission electron microscopy (TEM). The electron beam serves as a “light” source to initiate the catalytic reaction and a “water-in-salt” aqueous solution is employed as the electrolyte. The observation reveals that bubbles are generated preferentially residing near the {110} facet of a rutile TiO2 nanorod under a low electron dose rate (9.3–18.6 e-/Å2·s). These bubbles are ascribed to hydrogen gas generated from the pseudo-photocatalytic water splitting. As the electron beam current density increases to 93 e-/Å2 ·s, bubbles are also found at the {001} and {111} facets as well as in the bulk liquid solution, demonstrating the dominant effects of water electrolysis by electron beam under higher dose rates. The facet-dependent pseudo-photocatalytic behavior of rutile TiO2 nanorods is further validated using density functional theory (DFT)calculation. Our work establishes a facile liquid cell TEM setup for the study of pseudo-photocatalytic water splitting and it may also be applied to investigation of other photo-activated phenomena occurring at the solid-liquid interfaces
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