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11.
Heat treatment of polyacrylonitrile (PAN) leads to products with semiconductor-to-metal range of conductivities. The electrical
properties of these materials are further modified by ion implantation. The conductivity, 1×10–7 (Ω cm)–1, of heat treated PAN at 435°C (PAN435) increases upon ion implantation with As+, Kr+, Cl+ or F+, reaching the maximum value of 8.9×10–1 (Ω cm)–1 at a dose of 5×1016 ion/cm2 and an energy of 200 KeV for the case of F+ implantation. On the other hand, ion implantation in the more conducting heat-treated PAN at 750 °C (PAN750) leads to a decrease
in the electrical conductivity. It is shown that the conductivity modifications are primarily due to structural rearrangements
induced by the energetic ions. Specific chemical doping contribution to conductivity is noted for halogen implantation in
PAN435. The temperature dependence of conductivity of PAN heat treated at 750°C suggests a two path conduction, namely a three
dimensional variable range hopping conduction and a metallic conduction. After ion implantation, the conductivity-temperature
dependence is interpreted in terms of a variable range hopping conduction mechanism.
Received: 25 August 2000 / Reviewed and accepted: 28 August 2000 相似文献
12.
The influence of reusing ‘Formtex’ controlled permeability formwork on strength and durability of concrete 总被引:2,自引:1,他引:1
The effects of the reuse of ‘Formtex’ Controlled Permeability Formwork (CPF) liner on strength and durability properties of
concrete were investigated at two different water-cement ratios and the results are reported in this paper. Test blocks were
cast using the CPF on one side and impermeable formwork (IF) on the opposite side of the mould so that direct comparisons
could be made between the two. The strength was assessed using the Limpet pull-off tester and both the air permeability and
the water absorption (sorptivity) were measured using the Autoclam Permeability System. Both these instruments measured the
‘covercrete’ properties. In addition, cores cut from the test specimens were subjected to an accelerated carbonation test
and a chloride exposure test. The results showed that the ‘Formtex’ CPF increases the surface strength and the durability
of concrete compared to the IF. There was an almost complete elimination of blowholes. The permeability of concrete decreased
and its resistance to the ingress of both carbon dioxide and chlorides increased when CPF was used. The beneficial effects
of the Formtex CPF were most evident in concrete of higher water-cement ratio. With the reuse of the Formtex liner twice,
that is a total of three uses, the performance of the CPF to improve the properties of concrete remained almost the same.
In this research the CPF liner was cleaned thoroughly between each use, which must be adhered to for site applications for
reproducing the beneficial effects observed in the laboratory. 相似文献
13.
Imad A. Basheer 《Computer-Aided Civil and Infrastructure Engineering》2000,15(6):445-463
Classic constitutive modeling of geomaterials based on the elasticity and plasticity theories suffers from limitations pertaining to formulation complexity, idealization of behavior, and excessive empirical parameters. This article capitalizes on the modeling capabilities of neural networks as substitutes for the classic approaches. The neural network–based modeling overcomes the difficulties encountered in understanding the underlying microscopic processes governing the material's behavior by redirecting the efforts into learning the cause-effect relations from behavioral examples. Several methodologies are presented and cross-compared for effectiveness in approximating a theoretical hysteresis model resembling stress-strain behavior. The most effective methodology was used in modeling the constitutive behavior of an experimentally tested soil and produced models that simulated the real behavior of the soil with high accuracy. Although these models are empirical, they are retrainable and thus, unlike classic constitutive modeling techniques, can be revised and generalized easily when new data become available. 相似文献
14.
The segregated storage problem consists of determining a minimum cost distribution of products among compartments such that only one product may be stored in a given compartment. This paper explores the computational aspects of using branch and bound methods to solve this problem. Such methods were first suggested for this problem by White and Francis. A variety of approaches are tested, utilizing heuristic node selection and branching decision rules. Three heuristics are also presented which generate solutions for use as initial upper bounds for improving efficiency of the branch and bound procedure or as solutions for very large problems. 相似文献
15.
Jamil Ahmad Wajahat Ur Rehman Shaik Khadheer Basha Basheer Ahamed Kuppanna Chidambaram 《Polymer-Plastics Technology and Engineering》2019,58(4):366-383
Polyamide-b-ethylene (Pebax) is a promising material for membrane-based gas separation application with excellent CO2 capturing potential. Pebax is a rubbery elastomer which offers good mechanical support with its hard crystalline phase and excellent gas transport through its amorphous polyether phase. This review article includes recent advances in Pebax based membrane synthesis, solvent selection for membrane synthesis, compatible fillers with Pebax matrix and the improved gas separation performance of the prepared membranes. The literature review shows that Pebax based membranes are a good candidate for separation of CO2 from flue gases and can be used for commercial applications. 相似文献
16.
A. Basheer S. M. Tauseef Tasneem Abbasi S. A. Abbasi 《Journal of Failure Analysis and Prevention》2018,18(1):83-91
A new method, RIsk and DIstance Minimization in Process Units Siting (RIDIMPUS), is presented with which hazardous units can be sited in a chemical process facility in a manner that the risk of accidents involving the hazardous units as also the cost of spacing the units is minimized. To achieve this, safety and cost factors were modeled using various governing parameters and then expressions were designed to integrate the safety and the economic concerns to form model equations, inequalities and disjunctions. The resulting nonlinear programming model is solvable by using algorithms and solvers on any common desktop computer, thereby providing an optimal and prompt solution. 相似文献
17.
Cherakkathodi Sudheesh Kappat Valiyapeediyekkal Sunooj K.U. Anjali Basheer Aaliya Muhammed Navaf Sunny Kumar Vallayil Appukuttan Sajeevkumar Johnsy George 《International Journal of Food Science & Technology》2020,55(6):2391-2398
Physico-chemical, retrogradation, rheological properties and in vitro digestibility of lysine incorporated kithul starch modified by annealing, heat moisture treatment and its combinations were studied. LS-AHMT (annealed-heat moisture treated lysine incorporated kithul starch) exhibited lowest amylose leaching. LS-AHMT showed significantly (P ≤ 0.05) higher relative crystallinity. LS-ANS (annealed lysine incorporated kithul starch), LS-HMT (heat moisture treated lysine incorporated kithul starch) and LS-AHMT formed more weak gel by the effect of annealing, heat moisture treatment and its combination. LS-AHMT showed lowest pasting viscosities, G′ and G″ values among the modified kithul starch, which indicates its lower retrogradation properties. In vitro digestibility of kithul starch decreased after modifications and LS-ANS, LS-HMT and LS-AHMT showed significantly higher resistant starch content. The current study showed that annealing, heat moisture treatment and its combination on NS-LS (lysine incorporated kithul starch) effectively modified kithul starch properties. 相似文献
18.
Naqvi Nuzhat Abbasi Aliya Tabassum Hussain Rasheed Khan M. Aihab Ahmad Basheer 《Wireless Personal Communications》2018,103(2):1563-1585
Wireless Personal Communications - This paper presents a Multilayer Partially Homomorphic Encryption Text Steganography, an invisible approach for covert communication. Existing text-based schemes... 相似文献
19.
Novel Azo dyes possessing varying conjugation lengths and different extents of electron cloud delocalisation were synthesised and characterised and explored as sensitizers for dye-sensitised solar cells (DSSC). The envisaged azo dyes comprising of electron withdrawing and electron-donating moieties which are linked through conjugation bridges of varying lengths facilitated the prevalence of push–pull mechanism in the molecules. Optimisation of the geometry were performed for the synthesised compounds using B3LYP/ 6-31?+?G (d,p) level of density functional theory and their computed optical absorption and band gaps were validated with experimental results. The dyes exhibited molar extinction coefficients in the range of 3.2?×?104 to 4.2?×?104?mol?1?Lcm?1. The highest occupied molecular orbital (HOMO) was located between ?5.53 and ?5.03?eV for the various sensitizers synthesised and their lowest unoccupied molecular orbital (LUMO) was located between ?2.86 and ?3.08?eV. HOMO–LUMO gaps were in the range of 2.02–2.67?eV. Fill factor of the cells varied from 28% to 32% and the power conversion efficiencies ranged from 0.4% to 2.7%. This is the first time reporting of a systematic investigation, correlating the influence of nature and position of substituent, extending of conjugation and geometry of sensitizers on the photo physical properties of the sensitizers and the photovoltaic performance of corresponding DSSC.Highlights
The article focuses on push–pull azo dyes and were explored as promising candidate sensitizers for low cost dye-sensitised solar cells (DSSC).
The effect of chemical structure, extend of conjugation and geometry of the sensitizer on the photo physical properties of the sensitizers and the photovoltaic performance of DSSC were analysed.
20.
Structural Characteristics and Electrical Conductivity of Spark Plasma Sintered Ytterbia Co‐doped Scandia Stabilized Zirconia
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Vandana Shukla Ashutosh Kumar Ishamol Labbaveettil Basheer Kantesh Balani Anandh Subramaniam Shobit Omar 《Journal of the American Ceramic Society》2017,100(1):204-214
The effect of replacing Sc2O3 with Yb2O3 on the structural and electrical properties of xYb2O3–(12–x)Sc2O3–88ZrO2 has been investigated. Spark plasma sintering technique is employed to fabricate dense bulk samples from the nano‐sized powders. X‐ray diffraction and transmission electron microscopy performed on pellets indicate the existence of cubic and rhombohedral phases in 12ScSZ, and a single cubic phase in all the co‐doped compositions. However, Raman spectroscopic studies suggest the presence of a metastable tetragonal t″‐phase along with rhombohedral phases in 12ScSZ, whereas a single cubic phase in all the co‐doped compositions. Significant enhancement in the conductivity of grain and grain boundary is observed on replacing Sc2O3 with Yb2O3. In the intermediate temperature range, 1Yb11ScSZ exhibits the highest, while 12ScSZ shows the lowest conductivity values, which is attributed to corresponding phases present in that range. Through co‐doping with >1 mol% Yb2O3 leads to conductivity decrease, but the value remains higher than that of 12ScSZ. A sharp conductivity change is observed in 12ScSZ and 1Yb11ScSZ samples, which is attributed to partial phase transition as well to the formation of cation‐vacancy complexes. In this work, the beneficial effect of Yb2O3 co‐doping in 12ScSZ on the phase and conductivity has been highlighted. 相似文献