The study deals with amplification of a propagating slow wave interacting with an annular hollow electron beam in a helix slow wave structure (SWS). The role of thermal plasma density in a ratio of the axial pointing flux in the plasma region is also investigated. This ratio is small for lower plasma densities. The effects of the variations of the hollow electron beam velocity on the normalized growth rate and the poynting flux ratio at the hybrid mode frequency are presented. The maximum gain is obtained in the frequency of hybrid mode and the poynting flux ratio reaches its maximum value at the hybrid mode frequency. Also is analyzed the trend of changes for the normalized growth rate for a different beam velocities. The results show that for all beam velocities the maximum growth rate is for hybrid mode frequencies. The numerical method used in this paper is complex transcendental. Manuscript profile

Impacts of the liquid environment on the characteristics of pulsed laser ablation (PLA) synthesized tungsten (W) nanostructures have been investigated. High purity W target was irradiated by the fundamental wavelength of a Q-switched Nd:YAG laser of 7 ns pulse width and 1 J/cm2 laser fluence in different liquid environments including distilled water, ethanol, acetone, and cetrimonium bromide (CTAB) solutions. Structural, chemical, and optical properties of W nanoparticles (NPs) were characterized by different spectroscopic and imaging techniques. FTIR spectra indicate the formation of a bond between W and O in the synthesized NPs, and XRD patterns confirm producing W and WO3 composite NPs in all liquid environments. The excitonic/plasmonic absorption peak of W/WO3 NPs were occurred in the absorption spectra of all samples. The largest particles with the lowest adhesion were synthesized in acetone solution, and adding CTAB surfactant to distilled water reduced the adhesion of NPs as is depicted by FESEM. TEM images confirm the formation of core-shell W/WO3 nanostructures in distilled water. The PL spectra present band-to-band transitions and oxygen vacancies of WO3. Manuscript profile

Thermal plasma treatment is considered as a suitable alternative for the treatment of highly-hazardous wastes such as industrial, radioactive and medical waste. Therefore, a Plasma-Gasification-Melting (PGM) system for treatment of Chemical and Pharmaceutical Wastes (CPW) with a capacity of 1 ton/day is developed using a melting and gasification furnace equipped with two non-transferred thermal plasma torches. In this article, the whole method of chemical and pharmaceutical waste disposal is presented along with exhaust gas analysis, and slag and energy balance approach for improving the relevant technology process. It is successfully demonstrated that the thermal plasma process converts chemical and pharmaceutical wastes into harmless slag. Also, the associated emission level of air pollutants is shown to be very low. The synthetic gas produced can be used as a source of energy. (11.7 Nm3 / hr for CO and 16.4 Nm3 / hr for H2). The total power consumption of the system is 120 k W including 90 kW for thermal plasma torch and 30 kW for utilities with natural gas flow rate of 1.3 Nm3/hr. Manuscript profile

Preparation of graphene decorated MOF-5 nanocomposite by pulsed laser ablation (PLA) method in liquid environment has been investigated for the first time. Firstly, MOF-5 nanostructures were synthesized by irradiating a high-purity zinc (Zn) plate in dimethylformamide (DMF) solution containing terephthalic acid ligand with Nd:YAG pulsed laser. Using the fundamental wavelength of Nd:YAG laser at 1046 nm and pulse width of 7 ns, three samples of MOF-5 nanostructures were produced in the solutions with three ligand concentrations. Then, by laser ablation of a graphite target in the MOF-5 nanostructures suspensions, graphene/MOF-5 nanocomposites were produced. Furthermore, the antibacterial activity of the samples was evaluated against Escherichia coli (E. coli) as a gram-negative and Staphylococcus aureus (S. aureus) as a gram-positive bacterium. Morphology of MOF-5 nanostructures was modified due to presence of graphene nanosheets in the structure of nanocomposite. TEM images show that square shape MOF-5 particles were located on the surface of graphene nanosheets. Concentration of synthesized samples was increased with increasing the ligand concentration in the liquid environment of ablation. And stronger antibacterial effects of nanocomposites were observed against the gram-negative bacteria due to their gravitation of opposite charges. Manuscript profile

We present a new theoretical model for analyzing the impact of higher order modes on transverse mode instability in bent Yb-doped fiber amplifiers. The model indicates a comparative analysis of mode instability using the normalized propagation constant in straight and bent fibers amplifiers. The impact of different bending radii, in bent fibers is investigated on the normalized propagation constant. The results are then compared with the straight fibers. Considering all the existed modes, the behavior of mode instability in the fibers with different V-numbers are simulated and explained physically. Manuscript profile

AbstractLangmuir probe measurements are performed in cylindrical dc glow discharge plasma. Plasma was generated in an evacuated glass tube, with circular plane disk electrodes. Measurements were carried out at different points along the axis of tube for different working pressures of pure argon and mixture of argon–oxygen gasses to obtain the plasma density and temperature as well as plasma and floating potentials. Variation of discharge potential as a function of discharge pressure for both plasmas is observed. It is shown that electron temperature, plasma potential, and floating potential in constant current mode and constant pressure are increased from cathode to anode on the axial points of the discharge tube, while electron density is decreased. To sustain the discharge process after adding oxygen to plasma, higher voltage is required since electrons are more energetic at lower density. Manuscript profile

AbstractA direct three-dimensional model to study the wakefield in underdense magnetized plasma is introduced. The model is based on an analytic procedure by Laplace transformation for calculating the magnetized plasma wake equations. Wakefield is excited using a high-intensity ultrashort laser beam. In the presence of external magnetic field perpendicular to the direction of the laser pulse propagation direction, plasma electrons rotate around the magnetic field lines, leading to the generation of an electromagnetic component of the plasma wakes at plasma frequency. This component is polarized perpendicularly to the direct current magnetic field lines and propagates in the forward direction and normal direction with respect to the laser pulse propagation direction, both perpendiculars to the direction of the applied magnetic field. Intensity of the radiation in different plasma densities and different magnetic field strengths has been observed. Manuscript profile

AbstractSwanepoel method is employed for spectroscopic determination of optical properties of Cu3N thin film using transmittance data. Investigated films have been deposited using reactive magnetron sputtering system. Deposition time was 9 to 21 min. Refractive index, absorption coefficient, and bandgap energy of the samples are determined. Thickness of the films is calculated by Swanepoel method, and result is compared with the thickness of the films measured by profilmeter. It is shown that Swanepoel method is a reliable way to calculate the optical constants of thin films when the transmittance spectrum of the film is influenced by wavelike patterns due to reflection of the probe beam from different interfaces. Manuscript profile

AbstractIn this experimental study, the effect of dye concentration on the optical properties of red-BS dye-doped polyvinyl alcohol (PVA) thin films is investigated. Three thin film samples with different concentration of red-BS dye were prepared by spin-coating method on the glass substrate. Using transmission and reflection spectrum of films, their optical parameter such as refractive index, absorption coefficient, and dielectric function are extracted and the effect of dye impurity on theses parameters has been studied. The band gap energy of samples is calculated using Tauc method. Band gap energy of samples is decreased by increasing the concentration of dye impurity in PVA films. Manuscript profile

AbstractIn this paper, a theoretical investigation has been made of obliquely propagating dust acoustic solitary wave (DASW) structures in a cold magnetized dusty plasma consisting of a negatively charged dust fluid, electrons, and two different types of nonthermal ions. The Zakharov–Kuznetsov (ZK) and modified Zakharov–Kuznetsov (MZK) equations, describing the small but finite amplitude DASWs, are derived using a reductive perturbation method. The combined effects of the external magnetic field, obliqueness (i.e. the propagation angle), and the presence of second component of nonthermal ions, which are found to significantly modify the basic features (viz. amplitude, width, polarity) of DASWs, are explicitly examined. The results show that the external magnetic field, the propagation angle, and the second component of nonthermal ions have strong effects on the properties of dust acoustic solitary structures. The solitary waves may become associated with either positive potential or negative potential in this model. As the angle between the direction of external magnetic field and the propagation direction of solitary wave increases, the amplitude of the solitary wave (for both positive potential and negative potential) increases. With changing this angle, the width of solitary wave shows a maximum. The magnitude of the external magnetic field has no direct effect on the solitary wave amplitude. However, with decreasing the strength of magnetic field, the width of DASW increases. Manuscript profile

In this study, the efficiencies of seed priming with electromagnetic field (0, 2, 4, and 6 mT; 30 minutes daily for 3 days) were investigated in Salvia nemorosa. The exposure to electromagnetic filed led to significant increases in biomass accumulation (mean=53.6 %). Electromagnetic filed treatments significantly increased K, Ca, Mg, and Fe contents in leaves by mean 39.5 %. The electromagnetic filed treatments at all applied intensities increased both chlorophyll and carotenoid contents. Moreover, the electromagnetic filed- treated seedlings had significantly higher protein levels (mean=47 %) than the control. The applications of electromagnetic filed treatments induced peroxidase activities (mean=34.5 %) in leaves. However, these treatments reduced the activities of superoxide dismutase and catalase enzymes. The PAL activities in the electromagnetic filed-treated seedlings were higher by 61 % over the control. With a similar trend, the electromagnetic filed treatments promoted flavonoid accumulations. These results support this hypothesis that the application of the electromagnetic field may improve plant growth and secondary metabolism. Further studies, especially at molecular levels may help to elucidate the complicated involved mechanisms. Manuscript profile

در این مقاله ابتدا به پلیمر PVA رنگینه قرمز(red BS dye)با مقادیر مختلف افزوده شده و سپس فیلمهایی از آنها تهیه گردیده است. از این فیلمها طیف FTIR گرفته شده تا تاثیر رنگینه افزوده شده بر روی ساختار پلیمر مورد بررسی قرار گیرد. سپس با استفاده طیف عبوری و بازتابشی ضریب شکست خطی نمونه بدست آمده و مورد مقایسه قرار گرفته اند. علاوه بر این نمودار ضریب جذب نمونه ها بر حسب انرژی فوتونی تابیده تهیه گردیده و بررسی شده است. همچنین گاف انرژی مربوط به هر یک از نمونه ها نیز به دست امده است. در ادامه کار نمودارهای ضریب شکست و ضریب خاموشی بر حسب انرژی فوتون برای هر یک از نمونه ها رسم شده و در نهایت انرژی های پاشندگی برای هر یک از آنها محاسبه شده است. Manuscript profile

از روش کندگی لیزری تپی (PLA) برای نخستین بار برای سنتز نانوچندسازه‌های گرافن و چارچوب فلز-آلی مبتنی بر بیسموت(Bi-MOF) در محیط مایع استفاده شد. در این کار، نانوساختارهای Bi-MOF با کندگی لیزری یک هدف بیسموت به عنوان مرکز اتصال، بنزن 5،3،1-تری کربوکسیلیک اسید (BTC) به عنوان یک لیگاند پل زن، و متانول (MeOH) و دی متیل فرمامید (DMF) به عنوان حلال سنتز شدند. در مرحله نخست سه نمونه نانو ساختار Bi-MOF در سه غلظت متفاوت لیگاند تولید شد. سپس نانوچندسازه های گرافن MOF- با کندگی لیزر تپی Nd:YAG از هدف گرافیت در سه نمونه نانوساختار Bi-MOF به دست آمده، تولید شد. نانوچندسازه ها با پراش پرتو ایکس (XRD) برای مطالعه ساختار بلوری، طیف سنجی فروسرخ تبدیل فوریه (FTIR) برای تعیین گروه های عاملی، میکروسکوپ الکترونی روبشی گسیل میدانی (FESEM) و میکروسکوپ الکترونی عبوری (TEM) برای ریخت شناسی، طیف‌سنجی مرئی-فرابنفش (UV-Vis) برای تعیین فاصله نوار ارزیابی شدند. فعالیت پادباکتری نمونه ها در برابر باکتری اشرشیاکلی (E. coli) به عنوان باکتری گرم منفی و استافیلوکوکوس اورئوس (S. aureus) به عنوان باکتری گرم مثبت بررسی شد. برپایه نتیجه ها، کندگی لیزر تپی روشی دوستدار محیط زیست و قادر به تولید نانوچندسازه های گرافن - MOF در مدت زمان کوتاه است. این نانوساختارها می‌توانند کاربردهای گسترده‌ای از جمله در بی اثرسازی باکتری های مضر داشته باشند. Manuscript profile