URBAN PLANNING WITH THE AID OF FACTOR ANALYSIS APPROACH: THE CASE OF ISFAHAN MUNICIPALITY

Nowadays municipalities play an important role in offering urban services to the citizens. To investigate performance of regional municipalities, different data on living situation must be considered. Thus, we face a multivariate analysis. In this research regarding capabilities of "Factor Analysis" technique in the area of multivariate analysis, we used this technique to construct latent factors for comparison of different districts of a city. Along these lines we examined the real case of Isfahan municipality. Isfahan is a major city in Iran. The results of our analysis show that instead of evaluating different variables in each region we can concentrate on two simple and informative criteria representing common welfare situation and development situation in each region. The proposed approach shows which factors are more important for each region of the city and how different regional municipalities can apply cost effective policies to improve their performance.Regional Municipalities, Multivariate Analysis, Factor Analysis, Isfahan.

Temperature-dependent contact resistances in high-quality polymer field-effect transistors

Contact resistances between organic semiconductors and metals can dominate the transport properties of electronic devices incorporating such materials. We report measurements of the parasitic contact resistance and the true channel resistance in bottom contact poly(3-hexylthiophene) (P3HT) field-effect transistors with channel lengths from 400 nm up to 40 $\mu$m, from room temperature down to 77 K. For fixed gate voltage, the ratio of contact to channel resistance decreases with decreasing temperature. We compare this result with a recent model for metal-organic semiconductor contacts. Mobilities corrected for this contact resistance can approach 1 cm$^{2}$/Vs at room temperature and high gate voltages.Comment: 10 pages, 4 figures, accepted to Appl. Phys. Let

Doping dependent charge injection and band alignment in organic field-effect transistors

We have studied metal/organic semiconductor charge injection in poly(3-hexylthiophene) (P3HT) field-effect transistors with Pt and Au electrodes as a function of annealing in vacuum. At low impurity dopant densities, Au/P3HT contact resistances increase and become nonohmic. In contrast, Pt/P3HT contacts remain ohmic even at far lower doping. Ultraviolet photoemission spectroscopy (UPS) reveals that metal/P3HT band alignment shifts dramatically as samples are dedoped, leading to an increased injection barrier for holes, with a greater shift for Au/P3HT. These results demonstrate that doping can drastically alter band alignment and the charge injection process at metal/organic interfaces.Comment: 5 pages, 4 figure

Nonlinear charge injection in organic field-effect transistors

Transport properties of a series of poly(3-hexylthiophene) organic field effect transistors with Cr, Cu and Au source/drain electrodes were examined over a broad temperature range. The current-voltage characteristics of the injecting contacts are extracted from the dependence of conductance on channel length. With reasonable parameters, a model of hopping injection into a disordered density of localized states, with emphasis on the primary injection event, agrees well with the field and the temperature dependence of the data over a broad range of temperatures and gate voltages.Comment: 7 pages, 7 figures, sub. to J. Appl. Phy

A Cross Layer Solution to Address TCP Intra-flow Performance Degradation in Multihop Ad hoc Networks

Incorporating the concept of TCP end-to-end congestion control for wireless networks is one of the primary concerns in designing ad hoc networks since TCP was primarily designed and optimized based on the assumptions for wired networks. In this study, our interest lies on tackling the TCP instability and in particular intra-flow instability problem since due to the nature of applications in multihop ad hoc networks, connection instability or starvation even for a short period of time can have a negative impact on the Quality of Service and may not be acceptable for the end user. Through a detailed analysis, it will be shown that the main causes of TCP intra-flow instability lies in overloading the network by sending more packets than the capacity of the channel. Based on this, the paper proposes a novel cross layer solution called “TCP Contention Control” that dynamically adjusts the amount of outstanding data in the network based on the level of contention experienced by packets as well as the throughput achieved by connections. The simulation results show TCP Contention Control can drastically improve TCP stability over 802.11 multihop ad hoc networks

Gated nonlinear transport in organic polymer field effect transistors

We measure hole transport in poly(3-hexylthiophene) field effect transistors with channel lengths from 3 $\mu$m down to 200 nm, from room temperature down to 10 K. Near room temperature effective mobilities inferred from linear regime transconductance are strongly dependent on temperature, gate voltage, and source-drain voltage. As $T$ is reduced below 200 K and at high source-drain bias, we find transport becomes highly nonlinear and is very strongly modulated by the gate. We consider whether this nonlinear transport is contact limited or a bulk process by examining the length dependence of linear conduction to extract contact and channel contributions to the source-drain resistance. The results indicate that these devices are bulk-limited at room temperature, and remain so as the temperature is lowered. The nonlinear conduction is consistent with a model of Poole-Frenkel-like hopping mechanism in the space-charge limited current regime. Further analysis within this model reveals consistency with a strongly energy dependent density of (localized) valence band states, and a crossover from thermally activated to nonthermal hopping below 30 K.Comment: 22 pages, 7 figures, accepted to J. Appl. Phy

Controlling charge injection in organic field-effect transistors using self-assembled monolayers

We have studied charge injection across the metal/organic semiconductor interface in bottom-contact poly(3-hexylthiophene) (P3HT) field-effect transistors, with Au source and drain electrodes modified by self-assembled monolayers (SAMs) prior to active polymer deposition. By using the SAM to engineer the effective Au work function, we markedly affect the charge injection process. We systematically examine the contact resistivity and intrinsic channel mobility, and show that chemically increasing the injecting electrode work function significantly improves hole injection relative to untreated Au electrodes.Comment: 5 pages, 2 figures. Supplementary information available upon reques

Interfacial charge transfer in nanoscale polymer transistors

Interfacial charge transfer plays an essential role in establishing the relative alignment of the metal Fermi level and the energy bands of organic semiconductors. While the details remain elusive in many systems, this charge transfer has been inferred in a number of photoemission experiments. We present electronic transport measurements in very short channel ($L < 100$ nm) transistors made from poly(3-hexylthiophene) (P3HT). As channel length is reduced, the evolution of the contact resistance and the zero-gate-voltage conductance are consistent with such charge transfer. Short channel conduction in devices with Pt contacts is greatly enhanced compared to analogous devices with Au contacts, consistent with charge transfer expectations. Alternating current scanning tunneling microscopy (ACSTM) provides further evidence that holes are transferred from Pt into P3HT, while much less charge transfer takes place at the Au/P3HT interface.Comment: 19 preprint pages, 6 figure