1,029 research outputs found
Graphene field-effect transistors based on boron nitride gate dielectrics
Graphene field-effect transistors are fabricated utilizing single-crystal
hexagonal boron nitride (h-BN), an insulating isomorph of graphene, as the gate
dielectric. The devices exhibit mobility values exceeding 10,000 cm2/V-sec and
current saturation down to 500 nm channel lengths with intrinsic
transconductance values above 400 mS/mm. The work demonstrates the favorable
properties of using h-BN as a gate dielectric for graphene FETs.Comment: 4 pages, 8 figure
The response of benthic foraminifer, ostracod and mollusc assemblages to environmental conditions: a case study from the Camalti Saltpan (Izmir-Western Turkey)
The subject of this report is benthic foraminifer populations preserved in the saltpan of Camalti in the Province of Izmir. High salinity in certain habitats of Ammonia tepida Cushman may be the primary cause of the high rate of twins and triplets as well as other morphological abnormalities recorded within this species (50 % as compared to an anomaly rate of 1 % in normal marine waters). Thicker cyst membrane developing in extremely saline environments may encourage twins and other morphological deformities by denying free movement of the offspring. Ecological factors such as heavy metal contamination of ambient waters as well as contamination by other wastes are also not ruled out as leading to such developmental anomalies. Of the 27 collected samples, Number 5 (that is closest to the sea) includes the typical marine foraminifers. Nonion depressulum (Walker & Jacob), Ammonia tepida Cushman and Porosononion subgronosum(Egger) are the dominant species in other samples. A total of 63 abnormal individuals (8 triplets, 24 twins, and 31 morphological anomalies) was found within seven of the 27 samples collected. Ten samples contained freshwater ostracods: Darwinula stevensoni(Brady and Robertson), Leptocythere lacertosa Hirschmann, Cyprideis torasa (Jones), Cyprideis (C.) anatolica Bassiouni, and Loxochoncha elliptica Brady. Among these samples (some of which contained only a few species of ostracods - and those limited in number of offspring), one had an unusually high ratio of healthy foraminifers vs those with anomalies. Worthy of note in another sample was a high abundance of molluscs. Among pelecypods, were found Ostrea edulis Linné, Lucinella divaricata (Linné), Pseudocama gryphina Lamarck,Cerastoderma edule (Linné), and Scrobicularia plana da Costa; and among gastropods were identified Hydrobi (Hydrobia) acuta(Draparnaud), Rissoa labiosa (Montagu), R. parva (da Costa), R. violacea Desmarest, Pirenella conica (Blainville), Bittium desayesi(Cerulli and Irelli), B. lacteum Philippi and B. reticulatum Philippi
Study of strong turbulence effects for optical wireless links
Strong turbulence measurements that are taken using real time optical wireless experimental setups are valuable when studying the effects of turbulence regimes on a propagating optical beam. In any kind of FSO system, for us to know the strength of the turbulence thus the refractive index structure constant, is beneficial for having an optimum bandwidth of communication. Even if the FSO Link is placed very well-high-above the ground just to have weak enough turbulence effects, there can be severe atmospheric conditions that can change the turbulence regime. Having a successful theory that will cover all regimes will give us the chance of directly processing the image in existing or using an additional hardware thus deciding on the optimum bandwidth of the communication line at firsthand. For this purpose, Strong Turbulence data has been collected using an outdoor optical wireless setup placed about 85 centimeters above the ground with an acceptable declination and a path length of about 250 meters inducing strong turbulence to the propagating beam. Variations of turbulence strength estimation methods as well as frame image analysis techniques are then been applied to the experimental data in order to study the effects of different parameters on the result. Such strong turbulence data is compared with existing weak and intermediate turbulence data. Aperture Averaging Factor for different turbulence regimes is also investigated. © 2012 SPIE
Retreatment with anti-EGFR based therapies in metastatic colorectal cancer: impact of intervening time interval and prior anti-EGFR response.
BackgroundThis retrospective study aims to investigate the activity of retreatment with anti-EGFR-based therapies in order to explore the concept of clonal evolution by evaluating the impact of prior activity and intervening time interval.MethodsEighty-nine KRAS exon 2-wild-type metastatic colorectal patients were retreated on phase I/II clinical trials containing anti-EGFR therapies after progressing on prior cetuximab or panitumumab. Response on prior anti-EGFR therapy was defined retrospectively per physician-records as response or stable disease â„6 months. Multivariable statistical methods included a multiple logistic regression model for response, and Cox proportional hazards model for progression-free survival.ResultsRetreatment anti-EGFR agents were cetuximab (nâ=â76) or cetuximab plus erlotinib (nâ=â13). The median interval time between prior and retreatment regimens was 4.57 months (range: 0.46-58.7). Patients who responded to the prior cetuximab or panitumumab were more likely to obtain clinical benefit to the retreatment compared to the non-responders in both univariate (pâ=â0.007) and multivariate analyses (OR: 3.38, 95 % CI: 1.27, 9.31, pâ=â0.019). The clinical benefit rate on retreatment also showed a marginally significant association with interval time between the two anti-EGFR based therapies (pâ=â0.053). Median progression-free survival on retreatment was increased in prior responders (4.9 months, 95 % CI: 3.6, 6.2) compared to prior non-responders (2.5 months, 95 % CI, 1.58, 3.42) in univariate (pâ=â0.064) and multivariate analysis (HR: 0.70, 95 % CI: 0.43-1.15, pâ=â0.156).ConclusionOur data lends support to the concept of clonal evolution, though the clinical impact appears less robust than previously reported. Further work to determine which patients benefit from retreatment post progression is needed
Extending ballistic graphene FET lumped element models to diffusive devices
In this work, a modified, lumped element graphene field effect device model
is presented. The model is based on the "Top-of-the-barrier" approach which is
usually valid only for ballistic graphene nanotransistors. Proper modifications
are introduced to extend the model's validity so that it accurately describes
both ballistic and diffusive graphene devices. The model is compared to data
already presented in the literature. It is shown that a good agreement is
obtained for both nano-sized and large area graphene based channels. Accurate
prediction of drain current and transconductance for both cases is obtained
Quantum interference and Klein tunneling in graphene heterojunctions
The observation of quantum conductance oscillations in mesoscopic systems has
traditionally required the confinement of the carriers to a phase space of
reduced dimensionality. While electron optics such as lensing and focusing have
been demonstrated experimentally, building a collimated electron interferometer
in two unconfined dimensions has remained a challenge due to the difficulty of
creating electrostatic barriers that are sharp on the order of the electron
wavelength. Here, we report the observation of conductance oscillations in
extremely narrow graphene heterostructures where a resonant cavity is formed
between two electrostatically created bipolar junctions. Analysis of the
oscillations confirms that p-n junctions have a collimating effect on
ballistically transmitted carriers. The phase shift observed in the conductance
fringes at low magnetic fields is a signature of the perfect transmission of
carriers normally incident on the junctions and thus constitutes a direct
experimental observation of ``Klein Tunneling.''Comment: 13 pages and 6 figures including supplementary information. The paper
has been modified in light of new theoretical results available at
arXiv:0808.048
Photocurrent measurements of supercollision cooling in graphene
The cooling of hot electrons in graphene is the critical process underlying
the operation of exciting new graphene-based optoelectronic and plasmonic
devices, but the nature of this cooling is controversial. We extract the hot
electron cooling rate near the Fermi level by using graphene as novel
photothermal thermometer that measures the electron temperature () as it
cools dynamically. We find the photocurrent generated from graphene
junctions is well described by the energy dissipation rate , where the heat capacity is and is the
base lattice temperature. These results are in disagreement with predictions of
electron-phonon emission in a disorder-free graphene system, but in excellent
quantitative agreement with recent predictions of a disorder-enhanced
supercollision (SC) cooling mechanism. We find that the SC model provides a
complete and unified picture of energy loss near the Fermi level over the wide
range of electronic (15 to 3000 K) and lattice (10 to 295 K) temperatures
investigated.Comment: 7pages, 5 figure
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