209 research outputs found
Intrinsic charge transport on the surface of organic semiconductors
The novel technique based on air-gap transistor stamps enabled realization of
the intrinsic (not dominated by static disorder) transport of the
electric-field-induced charge carriers on the surface of rubrene crystals over
a wide temperature range. The signatures of the intrinsic transport are the
anisotropy of the carrier mobility, mu, and the growth of mu with cooling. The
anisotropy of mu vanishes in the activation regime at lower temperatures, where
the charge transport becomes dominated by shallow traps. The deep traps,
deliberately introduced into the crystal by X-ray radiation, increase the
field-effect threshold without affecting the mobility. These traps filled above
the field-effect threshold do not scatter the mobile polaronic carriers.Comment: 10 pages, 4 figure
Herzfeld instability versus Mott transition in metal-ammonia solutions
Although most metal-insulator transitions in doped insulators are generally
viewed as Mott transitions, some systems seem to deviate from this scenario.
Alkali metal-ammonia solutions are a brilliant example of that. They reveal a
phase separation in the range of metal concentrations where a metal-insulator
transition occurs. Using a mean spherical approximation for quantum polarizable
fluids, we argue that the origin of the metal-insulator transition in such a
system is likely similar to that proposed by Herzfeld a long time ago, namely,
due to fluctuations of solvated electrons. We also show how the phase
separation may appear: the Herzfeld instability of the insulator occurs at a
concentration for which the metallic phase is also unstable. As a consequence,
the Mott transition cannot occur at low temperatures. The proposed scenario may
provide a new insight into the metal-insulator transition in condensed-matter
physics.Comment: 9 pages, 4 figure
Plasma–liquid interactions: a review and roadmap
Plasma–liquid interactions represent a growing interdisciplinary area of research involving plasma science, fluid dynamics, heat and mass transfer, photolysis, multiphase chemistry and aerosol science. This review provides an assessment of the state-of-the-art of this multidisciplinary area and identifies the key research challenges. The developments in diagnostics, modeling and further extensions of cross section and reaction rate databases that are necessary to address these challenges are discussed. The review focusses on non-equilibrium plasmas
Chemistry of a polluted cloudy boundary layer
A one-dimensional photochemical model for cloud-topped boundary layers is developed which includes detailed descriptions of gas-phase and aqueous-phase chemistry, and of the radiation field in and below cloud. The model is used to interpret the accumulation of pollutants observed over Bakersfield, California, during a wintertime stagnation episode with low stratus. The main features of the observations are well simulated; in particular, sulfate accumulates progressively over the course of the episode due to sustained aqueous-phase oxidation of SO2Â in the stratus cloud. The major source of sulfate is the reaction S(IV) + Fe(III), provided that this reaction proceeds by a non radical mechanism in which Fe(III) is not reduced. A radical mechanism with SO3
− and Fe(II) as immediate products would quench sulfate production because of depletion of Fe(III). The model results suggest that the non radical mechanism is more consistent with observations, although this result follows from the absence of a rapid Fe(II) oxidation pathway in the model. Even with the non-radical mechanism, most of the soluble iron is present as Fe(II) because Fe(III) is rapidly reduced by O2
−. The S(IV) + Fe(III) reaction provides the principal source of H2O2 in the model; photochemical production of H2O2 from HO2 or O2(−I) is slow because HO2 is depleted by high levels of NOx. The aqueous-phase reaction S(IV) + OH initiates a radical-assisted S(IV) oxidation chain but we find that the chain is not propagated due to efficient termination by SO4
− + Cl− followed by Cl + H2O. A major uncertainty attached to that result is that the reactivities of S(IV)-carbonyl adducts with radical oxidants are unknown. The chain could be efficiently propagated, with high sulfate yields, if the S(IV)-carbonyl adducts were involved in chain propagation. A remarkable feature of the observations, which is well reproduced by the model, is the close balance between total atmospheric concentrations of acids and bases. We argue that this balance reflects the control of sulfate production by NH3, which follows from the pH dependence of the S(IV) + Fe(III) reaction. Such a balance should be a general characteristic of polluted environments where aqueous-phase oxidation of SO2 is the main source of acidity. At night, the acidity of the cloud approaches a steady state between NH3 emissions and H2SO4 production by the S(IV) + Fe(III) reaction. A steady state analysis suggests that [H+] at night should be proportional to (ESO
2/ENH
3)1/2Â where ESO
2Â and ENH
3 are emission rates of SO2 and NH3, respectively. From this analysis it appears that cloud water pH values below 3 are unlikely to occur in the Bakersfield atmosphere during the nighttime hours. Very high acidities could, however, be achieved in the daytime because of photochemical acid production by the gas-phase reactions NO2 + OH and SO2 + OH
Pathogenesis and treatment of gastric carcinoma: "An up-date with brief review"
Gastric cancer is one of the most common cancers and most frequent
causes of cancer-related deaths in the world. The overall survival rate
is 15-20%. Although the incidence is declining, its prognosis remains
poor. The etiological factors and pathogenesis of gastric cancer are
not yet fully understood. The integrated research in molecular
pathology clarified the details of genetic and epigenetic abnormalities
of cancer-related genes in the course of development and progression of
gastric cancer. Although epidemiological evidences indicate that
environmental factors play a major role in the carcinogenesis, the role
of immunological, genetic and immunogenetic factors are thought to
contribute to etiopathogenesis of gastric carcinoma. In addition to
better understanding of pathogenesis of gastric cancer, the incidence,
diagnostic studies and the therapeutic options have also undergone
important changes in the last decade. There is ongoing debate regarding
the role of adjuvant treatment. In advanced disease, palliation of
symptoms, rather than cure, is the primary goal of patient management.
Several combination therapies have been developed and have been
examined in phase III trials; however, in most cases, they have failed
to demonstrate a survival advantage over the reference arm. This review
summarizes the newer concepts of molecular biology on gastric
carcinogenesis and the new important recommendations for the management
of patient with gastric carcinoma
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