1,443 research outputs found
Chronic deep brain stimulation of subthalamic and anterior thalamic nuclei for controlling refractory partial epilepsy
Summary Objectives. Experimental data and case reports of intractable epilepsy patients treated with deep brain stimulation (DBS) of the internal nuclei suggest a considerable anticonvulsant effect. We intended to describe the results of DBS on subthalamic nuclei and anterior thalamic nuclei (STN and ATN) from our patients and to evaluate the long-term efficiency and safety of DBS for controlling intractable epilepsy. Methods. Six patients with refractory epilepsy and inadequate for surgery were implanted with DBS electrodes (3 in STN and 3 in ATN, respectively), switched on after a week of insertion followed by chronological observation. Seizure counts were monitored and compared with pre-implantation baseline. Results. There was significant clinical improvement in respect of reduction of seizure frequency as well as the alleviation of ictal severity in almost patients. The mean reduction in seizure frequency was 62.3% (49.1% from STN vs. 75.4% from ATN). Except one patient (patient 3) with accidental infection on the right anterior chest, no complication or withdrawal of DBS was seen during our study. Conclusion. DBS on STN and ATN demonstrated their clear efficiency and relative safety comparable or superior to previous studies during long term follow-up. Subsequent, well designed studies warrant the further increase of the knowledge about antiepileptic effect of DBS
Novel membrane bioreactor (MBR) coupled with a nonwoven fabric filter for household wastewater treatment
Conventional and modified membrane bioreactors (MBRs) are increasingly used in small-scale wastewater treatment. However, their widespread applications are hindered by their relatively high cost and operational complexity. In this study, we investigate a new concept of wastewater treatment using a nonwoven fabric filter bag (NFFB) as the membrane bioreactor. Activated sludge is charged in the nonwoven fabric filter bag and membrane filtration via the fabric is achieved under gravity flow without a suction pump. This study found that the biofilm layer formed inside the NFFB achieved 10 mg/L of suspended solids in the permeate within 20 min of initial operation. The dynamic biofilter layer showed good filterability and the specific membrane resistance consisted of 0.3-1.9 à 1012 m/kg. Due to the low F/M ratio (0.04-0.10 kg BOD5/m3/d) and the resultant low sludge yield, the reactor was operated without forming excess sludge. Although the reactor provided aerobic conditions, denitrification occurred in the biofilm layer to recover the alkalinity, thereby eliminating the need to supplement the alkalinity. This study indicates that the NFFB system provides a high potential of effective wastewater treatment with simple operation at reduced cost, and hence offer an attractive solution for widespread use in rural and sparsely populated areas. Crown Copyright © 2009
Possible Verification of Tilted Anisotropic Dirac Cone in \alpha-(BEDT-TTF)_2 I_3 Using Interlayer Magnetoresistance
It is proposed that the presence of a tilted and anisotropic Dirac cone can
be verified using the interlayer magnetoresistance in the layered Dirac fermion
system, which is realized in quasi-two-dimensional organic compound
\alpha-(BEDT-TTF)_2 I_3. Theoretical formula is derived using the analytic
Landau level wave functions and assuming local tunneling of electrons. It is
shown that the resistivity takes the maximum in the direction of the tilt if
anisotropy of the Fermi velocity of the Dirac cone is small. The procedure is
described to determine the parameters of the tilt and anisotropy.Comment: 4 pages, 4 figures, corrected Fig.
Intrinsic and Extrinsic Performance Limits of Graphene Devices on SiO2
The linear dispersion relation in graphene[1,2] gives rise to a surprising
prediction: the resistivity due to isotropic scatterers (e.g. white-noise
disorder[3] or phonons[4-8]) is independent of carrier density n. Here we show
that acoustic phonon scattering[4-6] is indeed independent of n, and places an
intrinsic limit on the resistivity in graphene of only 30 Ohm at room
temperature (RT). At a technologically-relevant carrier density of 10^12 cm^-2,
the mean free path for electron-acoustic phonon scattering is >2 microns, and
the intrinsic mobility limit is 2x10^5 cm^2/Vs, exceeding the highest known
inorganic semiconductor (InSb, ~7.7x10^4 cm^2/Vs[9]) and semiconducting carbon
nanotubes (~1x10^5 cm^2/Vs[10]). We also show that extrinsic scattering by
surface phonons of the SiO2 substrate[11,12] adds a strong temperature
dependent resistivity above ~200 K[8], limiting the RT mobility to ~4x10^4
cm^2/Vs, pointing out the importance of substrate choice for graphene
devices[13].Comment: 16 pages, 3 figure
A transverse current rectification in graphene superlattice
A model for energy spectrum of superlattice on the base of graphene placed on
the striped dielectric substrate is proposed. A direct current component which
appears in that structure perpendicularly to pulling electric field under the
influence of elliptically polarized electromagnetic wave was derived. A
transverse current density dependence on pulling field magnitude and on
magnitude of component of elliptically polarized wave directed along the axis
of a superlattice is analyzed.Comment: 12 pages, 6 figure
Exact eigenstate analysis of finite-frequency conductivity in graphene
We employ the exact eigenstate basis formalism to study electrical
conductivity in graphene, in the presence of short-range diagonal disorder and
inter-valley scattering. We find that for disorder strength, 5, the
density of states is flat. We, then, make connection, using the MRG approach,
with the work of Abrahams \textit{et al.} and find a very good agreement for
disorder strength, = 5. For low disorder strength, = 2, we plot the
energy-resolved current matrix elements squared for different locations of the
Fermi energy from the band centre. We find that the states close to the band
centre are more extended and falls of nearly as as we move away
from the band centre. Further studies of current matrix elements versus
disorder strength suggests a cross-over from weakly localized to a very weakly
localized system. We calculate conductivity using Kubo Greenwood formula and
show that, for low disorder strength, conductivity is in a good qualitative
agreement with the experiments, even for the on-site disorder. The intensity
plots of the eigenstates also reveal clear signatures of puddle formation for
very small carrier concentration. We also make comparison with square lattice
and find that graphene is more easily localized when subject to disorder.Comment: 11 pages,15 figure
Anti-fouling graphene-based membranes for effective water desalination
© 2018 The Author(s). The inability of membranes to handle a wide spectrum of pollutants is an important unsolved problem for water treatment. Here we demonstrate water desalination via a membrane distillation process using a graphene membrane where water permeation is enabled by nanochannels of multilayer, mismatched, partially overlapping graphene grains. Graphene films derived from renewable oil exhibit significantly superior retention of water vapour flux and salt rejection rates, and a superior antifouling capability under a mixture of saline water containing contaminants such as oils and surfactants, compared to commercial distillation membranes. Moreover, real-world applicability of our membrane is demonstrated by processing sea water from Sydney Harbour over 72 h with macroscale membrane size of 4 cm 2 , processing ~0.5 L per day. Numerical simulations show that the channels between the mismatched grains serve as an effective water permeation route. Our research will pave the way for large-scale graphene-based antifouling membranes for diverse water treatment applications
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