Mehdi Kazemi

Chemical resistance of natural fiber (wood flour, rice hulls, kenaf fiber, and newsprint) polypropylene composites was studied in terms of their weight loss and reduction of mechanical properties after 7 days immersion in chemical reagents. Composites containing 25 and 50% of various natural fibers and polypropylene were prepared and immersed in NaOH (10%), NaClO (bleach solution) (13%), HCl (10%), H2O2 (3%), soap solution (1%), and acetone. Results indicated that H2O2, soap solution, and acetone had very negligible effects on all composites. On the other hand, the effects of NaClO and HCl were found to be statistically significant. Different fibers exhibited different behaviors regarding their chemical resistance. Rice hulls composites were considerably affected by NaOH, whereas the same chemical reagent was ineffective on other fibers. The effects of bleach solution and HCl on the mechanical performance of the composites were found to be critical. Generally, it was concluded that bleach and acids had the highest effects on natural fiber polypropylene composites. POLYM. COMPOS. 27:563–569, 2006. © 2006 Society of Plastics Engineers

Abstract In gas and oil well completion, perforation channels must be made through the steel casing wall and cement and into the rock formation in the production zone to allow formation fluid to enter the well. This paper will present study results on using a pulsed CO2 laser to ...

Tapered plates are being increasingly used in modern engineering structures. The increasing use is due to the distributed flexural stiffness that helps reduce the weight of structural elements and improve the utilization of the material. The flexural stiffness, vibrational, and buckling capacities of these plates may be significantly increased by appropriate tapering. On the other hand, provision of openings in perforated plates which provide access for inspection, services, and maintenance, can greatly enhance the applicability of these members in many structures such as platforms, naval and aeronautical structures. Beside these advantages, openings result in a reduction of the buckling capacity, which should be taken into account. n this paper a new exact solution procedure using energy method based on modified vibrational mode shapes is formulated for the buckling analysis of simply supported rectangular plates of abruptly varying stiffness subjected to uniform edge stresses. It is shown that the vibrational mode shapes of a tapered plate is in fact a linear combination of various mode shapes of intact plates. This phenomenon is used to estimate the vibrational mode shapes of taper plates, and is then incorporated to evaluate the buckling loads.

The aims of this study are to identify Leishmania species and compare and validate internal transcribed spacers (ITS) polymerase chain reaction (PCR) assay against parasitological methods for diagnosing cutaneous leishmaniasis (CL). We used the ITS-PCR, parasite culture, and microscopic evaluation of stained smears on 155 specimens from suspected cases of (CL) patients who referred to Mashhad Health Centers (northeast Iran). The PCR indicated the sensitivity (98.8%), correctly diagnosing 86 of the 87 confirmed positive specimens. Microscopy and parasite culture alone showed 79.3% sensitivity (69/87 positive) and 86.2% sensitivity (75/87 positive), respectively, while microscopy and culture in combination improved sensitivity totally to 100% (87/87). The results also revealed that Leishmania tropica species is dominant (96.5%) in the studied regions. This study suggests that both the parasitological techniques reliably were used for the diagnosis of CL, and the ITS-PCR assay without using RFLP analysis is useful for identifying Leishmania species in the area.

Acute ischemia of the rectum is uncommon and usually occurs after aorto-iliac surgery. In this report, we present a case of acute ischemic proctosigmoiditis that developed from a brief episode of hypotension. An 85-year-old male presented to the emergency room with hypotension, mental confusion, and passage of maroon-colored stool. He was resuscitated and treated for presumed sepsis. Computerized tomography of the abdomen and pelvis displayed signs of acute inflammation of the distal colon and rectum. Endoscopic findings and microscopic examination of the rectal biopsy revealed changes consistent with acute ischemic proctosigmoiditis. An evaluation for infectious etiologies was negative. The patient's clinical condition improved over the next 24 h with supportive care. Involvement of the rectum is rare in ischemic colitis because of its abundant collateral blood supply. Acute ischemic proctosigmoiditis should be considered in the differential diagnosis of elderly patients with multiple co-morbidities presenting with hematochezia.

In this paper, a new model reference-decentralized robust adaptive-output feedback controller is proposed for the load frequency control (LFC) of large-scale power systems with unknown parameters. This control strategy requires only local input–output data and can follow random changes in the operating conditions. The controller is designed such that the trajectory errors and the control gains of each area remain uniformly bounded. In the proposed method, firstly an adaptive observer is designed to estimate the state variables and system parameters using local data only. Then a locally linear combination of the estimated states and the model reference states are used to design a robust adaptive-output feedback controller for each area. Simulation results for a three-area power system show that the proposed controller achieves good performance even in the presence of plant parameter changes and system non-linearities.