16,038 research outputs found
The influence of a single defect in composite gate insulators on the performance of nanotube transistors
The current through a carbon nanotube field-effect transistor (CNFET) with
cylindrical gate electrode is calculated using the nonequilibrium Greens
function method in a tight-binding approximation. The obtained result is in
good agreement with the experimental data. The space radiation and nuclear
radiation are known to cause defects in solids. The theoretical approach is
used to calculate the amplitude of the random-telegraph-signal (RTS) noise due
to a single defect in the gate oxide of a long channel p-type CNFET. We
investigate how the amplitude of the RTS noise is affected by the composite
structure of gate insulators, which contains an inner insulator with a
dielectric constant larger than 3.9 and an outer insulator with a dielectric
constant of 3.9 (as for SiO2). It is found that the RTS amplitude increases
apparently with the decreasing thickness of the inner gate insulator. If the
inner insulator is too thin, even though its dielectric constant is as large as
80, the amplitude of the RTS noise caused by the charge of Q = +1e may amount
to around 80% in the turn-on region. Due to strong effects of defects in
CNFETs, CNFETs have a potential to be used for detecting the space radiation or
nuclear radiation.Comment: 8 Figure
"Hard-scattering" approach to very hindered magnetic-dipole transitions in quarkonium
For a class of hindered magnetic dipole () transition processes, such as
(the discovery channel of the meson),
the emitted photon is rather energetic so that the traditional approaches based
on multipole expansion may be invalidated. We propose that a "hard-scattering"
picture, somewhat analogous to the pion electromagnetic form factor at large
momentum transfer, may be more plausible to describe such types of transition
processes. We work out a simple factorization formula at lowest order in the
strong coupling constant, which involves convolution of the Schr\"odinger wave
functions of quarkonia with a perturbatively calculable part induced by
exchange of one semihard gluon between quark and antiquark. This formula,
without any freely adjustable parameters, is found to agree with the measured
rate of rather well, and can also reasonably
account for other recently measured hindered transition rates. The
branching fractions of are also
predicted.Comment: v3; 5 pages, 1 figure and 1 table; title changed, presentation
improve
Efficiently computing and registering digitally reconstructed radiographs
Generation of digitally reconstructed radiographs (DRRs) is computationally expensive and has been cited as the rate-limiting step in the execution time of intensity-based two-dimensional/three-dimensional registration algorithms. This paper considers the problem of generating DRRs by conventional ray tracing. Experiments confirm that good quality reconstructions can be obtained using this approach in a few seconds. We evaluate the approach for automatic patient setup prior to radiotherapy treatment by performing intensity based 2D-3D registration using normalized cross correlation. Preliminary results using a pelvic CT data set show the method is accurate to about ±2 pixels (i.e. ±0.3 mm)
Electrical and optical properties of fluid iron from compressed to expanded regime
Using quantum molecular dynamics simulations, we show that the electrical and
optical properties of fluid iron change drastically from compressed to expanded
regime. The simulation results reproduce the main trends of the electrical
resistivity along isochores and are found to be in good agreement with
experimental data. The transition of expanded fluid iron into a nonmetallic
state takes place close to the density at which the constant volume derivative
of the electrical resistivity on internal energy becomes negative. The study of
the optical conductivity, absorption coefficient, and Rosseland mean opacity
shows that, quantum molecular dynamics combined with the Kubo-Greenwood
formulation provides a powerful tool to calculate and benchmark the electrical
and optical properties of iron from expanded fluid to warm dense region
Photon induced Lambda(1520) production and the role of the K^* exchange
We study the photon induced Lambda(1520) production in the effective
Lagrangian method near threshold, E_\gamma^{LAB}<2 GeV, and in the quark-gluon
string model at higher energies 3 GeV < E_\gamma^{LAB} < 5 GeV. In particular,
we study the role of the K^* exchange for the production of Lambda(1520) within
the SU(6) Weinberg-Tomozowa chiral unitary model proposed in Phys. Rev. D74
(2006) 034025. The coupling of the Lambda(1520) resonance to the N \bar K^*
pair, which is dynamically generated, turns out to be relatively small and,
thus, the K exchange mechanism dominates the reaction. In the higher energy
region, where experimental data are available, the quark-gluon string mechanism
with the K Regge trajectory reproduces both the energy and the angular
distribution dependences of the Lambda(1520) photo-production reaction.Comment: 20 pages and 6 page
Possible link of a structurally driven spin flip transition and the insulator-metal transition in the perovskite LaBaCoO
The complex nature of the magnetic ground state in LaACoO
(A = Ca, Sr, Ba) has been investigated via neutron scattering. It was
previously observed that ferromagnetic (FM) as well as antiferromagnetic (AFM)
correlations can coexist prior to the insulator-metal transition (IMT). We
focused on a unique region in the Ba phase diagram, from x = 0.17 - 0.22, in
which a commensurate AFM phase appears first with a propagation vector, k = (0,
-0.5, 0.5), and the Co moment in the (001) plane of the rhombohedral
lattice. With increasing x, the AFM component weakens while an FM order appears
with the FM Co moment directed along the (001) (=(111)) axis. By x
= 0.22, a spin flip to new FM component appears as the crystal fully transforms
to an orthorhombic (Pnma) structure, with the Co moments pointing along a new
direction, (001) (=(110)). It is the emergence of the magnetic Pnma
phase that leads to IMT.Comment: 5 page
Generation of Oligodendrocyte Progenitor Cells From Mouse Bone Marrow Cells.
Oligodendrocyte progenitor cells (OPCs) are a subtype of glial cells responsible for myelin regeneration. Oligodendrocytes (OLGs) originate from OPCs and are the myelinating cells in the central nervous system (CNS). OLGs play an important role in the context of lesions in which myelin loss occurs. Even though many protocols for isolating OPCs have been published, their cellular yield remains a limit for clinical application. The protocol proposed here is novel and has practical value; in fact, OPCs can be generated from a source of autologous cells without gene manipulation. Our method represents a rapid, and high-efficiency differentiation protocol for generating mouse OLGs from bone marrow-derived cells using growth-factor defined media. With this protocol, it is possible to obtain mature OLGs in 7-8 weeks. Within 2-3 weeks from bone marrow (BM) isolation, after neurospheres formed, the cells differentiate into Nestin+ Sox2+ neural stem cells (NSCs), around 30 days. OPCs specific markers start to be expressed around day 38, followed by RIP+O4+ around day 42. CNPase+ mature OLGs are finally obtained around 7-8 weeks. Further, bone marrow-derived OPCs exhibited therapeutic effect in shiverer (Shi) mice, promoting myelin regeneration and reducing the tremor. Here, we propose a method by which OLGs can be generated starting from BM cells and have similar abilities to subventricular zone (SVZ)-derived cells. This protocol significantly decreases the timing and costs of the OLGs differentiation within 2 months of culture
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