arash bahrami

Nonlinear dynamical system research is essential in science and engineering because it could be potentially employed to represent real-world phenomena.  Traditional methods rely on pre-defined models or computationally expensive simulations, limiting their applicability to only numerical data. In the present research, without any prior knowledge of the system, we suggest a novel way to build a linear representation of the Duffing oscillator by fusing the capabilities of deep neural networks with the Koopman operator. This recently established methodology makes it easier to estimate system parameters effectively and accurately predict the oscillator's future behavior. Our approach incorporates a modified training procedure that restricts the Koopman operator to a single linear layer within the neural network, improving interpretability and potentially reducing training complexity. This methodology not only simplifies nonlinear system analysis but also paves the way for advancements in predictive modeling across various fields. Notably, our method yields distinctive eigenvalues of the Koopman generator matrix, enabling the Koopman operator to exhibit robustness against noise and capture a spectrum of Duffing equation behaviors. This includes the precise prediction of periodic oscillations and the capturing of period-doubling bifurcation, all while maintaining tractability within the neural network framework.

The present article proposes the idea of multi-frequency excitation to harvest energy from low-frequency ambient vibrations. A nonlinear piezomagnetoelastic set-up, operating in the monostable mode, is considered. Due to nonlinearities being present in the system, a multi-frequency excitation gives rise to complicated phenomena such as combination and simultaneous resonances. We propose the idea of multi-frequency excitation and employing secondary resonances such as combination and simultaneous resonances occurring in nonlinear systems. Nonlinear differential equations governing the harvester dynamics are obtained based on the Hamilton extended principle and solved using the direct harmonic balance method. Numerical results are presented for an actual energy harvester subjected to a dual-frequency excitation. It is ascertained that multi-frequency excitation and exploiting combination and simultaneous resonance result in a significant enhancement in the harvester output voltage and power. It is also found that simultaneous resonance is more effective in improving the harvester performance than combination resonances

Nowadays, the use of herbal extracts for preparing various drugs is increasing because of the compatibility of the natural compounds present in the extracts with the human body. To this end, in this project, we studied Froriepia subpinnata (Ledeb.) Baill. in terms of its natural constituents and biological activities. The chemical composition of the hexane extract of F. subpinnata aerial parts was evaluated by the GC/MS analysis and 21 compounds (80.60%) of the total, including phytosterols and hydrocarbons, were identified. Also besides, a significant amount of flavonoids in the methanol extract of F. subpinnata (27.235 ± 0.048μg/mL) was estimated by the AlCl3 colorimetric method. Two flavonoids: rutin and catechin were identified in the methanol extract of F. subpinnata by HPLC analysis. The concentration of the flavonoids was evaluated (23.61 and 6.95) mg/g respectively. Antioxidant activity of the methanol extract of the species was also evaluated by the DPPH (1,1-diphenyl-2-picryl-hydrazyl) assay. We also investigated the antibacterial activity of methanol extract of F. subpinnata aerial parts against two bacteria Staphylococcus aureus and Escherichia coli by the MIC (Minimum Inhibition Concentration) method. The MIC values for S. aureus and E. coli were evaluated (0.031 and 1.0) mg/mL respectively. Our study shows that F. subpinnata possesses a variety of useful natural constituents, which makes it a promising plant for agricultural and medicinal uses.

Nonlinearities give rise to secondary resonances such as superharmonic and subharmonic resonances. The superharmonic resonance can activate large-amplitude responses when the excitation frequency is a fraction of the fundamental frequency of the system. These low frequency excitations are very beneficial for energy harvesting systems. This paper presents an analytical investigation of vibrational energy harvesters with superharmonic excitation in a pietzomagnetoelastic configuration. A piezomagnetoelastic power generator is assumed to operate in the monostable and bistable modes. Nonlinear differential equations governing the oscillations of the system is solved using the method of multiple scales. System responses to the superharmonic resonance including the cantilever tip displacement and the output voltage are determined. It is found that employing the superharmonic resonance can increase the amount of harvested energy in the system. The root mean square value of the output voltage is obtained for several cases in both monostable and bistable modes. The power generated in monostable and bistable modes is then compared through numerical simulations. It is observed that the bistable mode is more convenient for harvesting energy. In addition, a Rung-Kutta numerical scheme is used to solve the differential equations. It is shown that the perturbation solution is in a close agreement with the numerical solution.

In the present research, higher resonance frequencies are employed to improve the performance of the atomic force microscopy in the non-contact mode. Conventional models already used in the literature to study AFM microcantilever dynamics such as point-mass approach are not only incapable of modeling higher vibrational modes but also fail to predict microcantilever complicated dynamics with a sufficient accuracy. In this paper, the Hamilton’s extended principle is used to obtain equations governing the nonlinear oscillations of the AFM probe. Euler-Bernoulli beam assumptions and small deflection theory are assumed. The resulting partial differential equation is often converted to a set of ordinary differential equations and then this set is solved either numerically or based on perturbation methods. In the present research, however, the partial differential equation is attacked directly by a special perturbation technique. The accuracy of the present method is then verified by a combination of the Galerkin discretization scheme and a Rung - Kutta numerical solution. Finally, different behaviors of the AFM probe including static behavior, linear mode shapes and frequency response curves are investigated through several numerical simulations. It is found out that higher vibrational modes have smaller frequency shift. It is also found out that higher modes are faster in gathering surface information and also more sensitive to the excitation.

The present article investigates effects of the multi-frequency excitation on the output power of a piezomagnetoelastic energy harvester. The piezomagnetoelastic power generator is assumed to operate in the mono-stable mode. A perturbation technique based on the method of multiple scales is employed to develop an analytical solution to nonlinear differential equations governing the system dynamics. In addition, a Runge-Kutta numerical scheme is used to solve the differential equations. It is shown that the perturbation solution is in a close agreement with the numerical solution. The system response is determined for several cases including super-harmonic, combination and simultaneous resonances. The steady-state output voltage is then obtained for each case and compared with that of a single-frequency excitation. Due to nonlinearities present in the system, a multi-frequency excitation gives rise to complicated phenomena such as combination and simultaneous resonances. It is found out that exploiting these resonances can significantly increase the amount of energy harvested.

A comparison of the various microstructural and antimicrobial properties of emulsified films indicated significant differences. This study aimed to determine the effect of emulsion condition of oil phase on microstructure and anti-fungal properties of emulsified films based on carboxymethyl cellulose.

Emulsified films containing macro and nano emulsion of cinnamon essential oils were prepared at different concentrations (0.25%, 0.5% and 1 W/V). The anti-fungal test was performed in three replicate for each sample. The count of fungal spores was undertaken under the microscope by using the Neubarer cell until reaching the spore number of 106 CFU/ml. The films were cut using sterilized punch and placed on an inoculated culture medium. The plates were placed inside the incubator at 25°C for 24 hours. The output data were reported as the diameter of the non-growth halo and the anti-fungal index.

The decrease in the size of emulsion droplets below 100 nm resulted in a better dissemination from the cell wall of microorganisms and the anti-film efficiency improved. The microscopic images were an indicator of smooth surfaces for nano-emulsion films similar to control films, and the nano-droplets had better stability in the film matrix.

This study introduced a new kind of nano-active packaging film with some of its improved functional properties.

The purpose of the present research was a review of the effect of instructing negative emotion management skills on parents’ anxiety thoughts with autistic children. Method of research was quasi-experimental, and its type is a pretest-posttest design without control group. Population of the study consisted of all parents of children with pervasive developmental disorders in the “Zehne Ziba” Medical Center in Hamedan, that their number was 80. Initially, they asked parents by invitation, if they would be interested in attending to training courses in workshops of training negative emotion management, and they declared their readiness. Then, volunteer parents were assessed by the tests of anxiety thoughts, and were present parents with anxiety thoughts in this study which their number was 40. In this study anxiety thoughts questionnaire of Wells were used. The results showed that negative emotion management skills training were effective to reduce the parents’ anxiety thoughts with autistic children, and finally they were confirmed.

The aim of the present research was review of effect of instructing of negative emotion management skills on irrational beliefs in parents of autistic children. The study design was Method of research was quasi experimental, the type of pretestposttest design without control group. Population of the study were comprised to all parents of children with pervasive developmental disorders in the “zehne ziba” medical center in hamedan, that their number was 80. Initially were asked parents by invitation, if you are interested in attending to training courses in workshops of training of negative emotion management, declared their readiness. Then parents volunteer were assessed in briefing on tests of irrational beliefs, and were present parents with irrational beliefs in this study which their number was 40. In this study were used from irrational beliefs questionnaire of jones. The results showed that negative emotion management skills training affect to reduce irrational beliefs of parents of children with autism and were confirmed.

Critical thinking requires that change the thought ,exploring and postulate of students. So the purpose of this research is that Study the effects of Inquiry-based Instruction on critical thinking of students.
Research method was quasi-experimental with pretest-posttest design with an experimental group and a control group. The population of this study consisted of all girl students in fifth grade in hamedan city in 2014. Available sampling method was used in this study, 30 students were selected as subjects of research and perch 15 subjects in the control group and 15 subjects in the experimental group by random sampling. The instrument used in this study was California critical thinking questionnaire. The Inquiry-based Instruction was presented by the investigator in 20 sessions of 45 minutes for experimental group. Research data were analyzed by using covariance analysis.
Findings: The findings showed that there was significant difference between level of critical thinking of experimental group and control group in pretest and posttest. So Inquiry-based Instruction in science class had a positive effect on students’ critical thinking.
The results showed that Inquiry-based Instruction reiforce critical thinking of students in science class, so to the teachers of this lesson is recommended that attention to role of teaching to Inquiry-based Instruction to enhance their critical thinking.

The aim of this study was to evaluate the content of mercury (Hg), arsenic (As), nickel (Ni) and tin (Sn) in raw cow’s milk of traditional and industrial sites from 8 different sites in Arak City, Markazi Province, Iran. In this cross sectional study, a total of 32 samples were collected from sub-cities of Arak, Iran via subjective sampling method. Both industrial and traditional dairy farms were selected for sam­pling. Twenty-five gram of each sample was turned to ash in ovens for metal analyses including Hg, As, Ni and Sn by anatomic absorption spectrometer. The residue amounts of Hg and As were lower than permissible limit suggested by Codex Alimentarius, but for Ni and Sn it was higher only in one of the collection sites. The average concentra­tion of Hg was significantly higher (P<0.05) in traditional farms as compared to industrial farms. Be­sides, amounts of Sn was significantly high in the traditional farms (P<0.05). Further, a high contents Ni was detected in industrial farms (P<0.05). High Sn and Ni contents of some milk samples from this region might be potentially hazardous to consumers. Further, none of the other metals tested crossed permissible levels.

In this paper, we propose an optical millimetre wave radio-over-fibre (mm-wave RoF) system that uses a dual drive Mach Zehnder modulator (DD-MZM), which is biased at the maximum transmission biasing point, to generate an optical double sideband-suppressed carrier. The input to the DD-MZM are binary phase shift keying (BPSK), quadrature phase shift keying (QPSK), 8-phase shift keying (8-PSK) and 16-qaudrature amplitude modulation (16-QAM) schemes at a carrier frequency of 5 GHz with a rate of 2 Gsym/s and a local oscillator of 15 GHz obtain an mm-wave RoF signal at 30 GHz. We evaluate the generation and performances of the proposed system in terms of the power penalty, the error vector magnitude and the bit error rate (BER). Impairments including the self-phase modulation, chromatic dispersion and attenuation are considered when modelling the single mode fibre (SMF) based on the symmetrical split step Fourier method. We show that the power efficiency improves in the optimum region on average by ~11 dB, ~11 dB, ~12 dB and ~18 dB for BPSK, QPSK, 8-PSK and 16-QAM, respectively for the same optical launch power over 10, 30 and 50 km of SMF compared to the linear and non-linear regions.

Clinical signs, para-clinical tests and gross lesion can be used for identification of parasite contamination. In most parasite contamination the clinical signs are not obvious. Thus, para-clinical tests and gross lesion play important roles in identifying parasite disease as all organs of animals such as skin, eyes, kidneys, liver and digestive tube can be affected by the parasites. Consequently, there is a possibility to use the feces of animals in order to observe parasite ovum and larva to identify the disease.This research was conducted from May to September 2011, and the number of 250 faecal samples of pigeon from mixed companion birds keeping in the cages. Faecal samples were examined by direct smear method whereas egg per gram (EPG) was counted by modified McMaster technique and centrifugal flotation method using Sheather’s saturated sugar solution. In this study, Raillietina spp, Tetramers, Sygnamus, Capillaria, Ascaridia colombae and oocyst protozoa, Phthiraptera, Ceratophyllus columbae contamination were studied and the frequency were found to be 24%, 8%, 9%, 14%, 4%, 7%, 8% and 6% respectively. The result of this study and the finding from other studies indicates that pigeons could be less susceptible to mixed infections as compared to chickens.

In National University’s examination applicants must access some valid information sources by which they must be guided properly in this critical stage. This paper therefore, aims to review and assess the applicants’ information needs in Tehran. 352 individuals of those who were qualified for university in Tehran in 2006 were randomly selected as the samples. In order to collect required data a questionnaire was used. Both validity and reliability of the research instrument were examined. Based on measurement scale, data were analyzed using different statistics models including factor analysis. Findings revealed that the information needs of applicants include using instructional software, information about disciplines, universities and the criteria of academic admission and selection, information about and accesses to additional and relevant exam’s sources, guidelines for filling in required forms and its deadlines, planning methods for studying and technical points about field selection, and so on. The results also suggested that although there was not a significant difference between the information needs of applicants in terms of their major field of study and type of their diploma, but their needs according to their gander were different.

The present research is based on the application of system dynamics in internal evaluation. It aims to present a model in which policies and factors affecting quality in educational departments are investigated and determined, using system dynamics methodology. In the first step, factors having an impact on the quality of departments are selected based on relevant research theories, previous studies and factor analysis of departments. The factors include: faculty members, students,… members of the department, students, graduates, admitted students, research, teaching and learning educational programs, budget and educational and research equipment and facilities. In the second step, a general model is suggested to simulate the behavior of a department according to variables relevant to each factor. Then, the structural and behavioral validity of the model is tested against departmental hypothetical data. Finally, the simulated model is applied over a four-year span of time. Results indicate an improving trend in the quality of the departments supposed. The model can be used for analysis of not only the efficiency and effectiveness of the policies proposed by decision-makers but also the effectiveness of each variable in Promotion of the quality of a department. Therefore, such a model provides a simulating tool for managers and decision-makers to test and assess their policies and strategies.