Additional degree of freedom in phased-MIMO radar signal design using space-time codes

Vahdani, Roholah,Bizaki, Hossein Khaleghi,Joshaghani, Mohsen Fallah Electronics and Telecommunications Research Instit 2021 ETRI Journal Vol.43 No.4

In this paper, an additional degree of freedom in phased multi-input multi-output (phased-MIMO) radar with any arbitrary desired covariance matrix is proposed using space-time codes. By using the proposed method, any desired transmit covariance matrix in MIMO radar (phased-MIMO radars) can be realized by employing fully correlated base waveforms such as phased-array radars and simply extending them to different time slots with predesigned phases and amplitudes. In the proposed method, the transmit covariance matrix depends on the base waveform and space-time codes. For simplicity, a base waveform can be selected arbitrarily (ie, all base waveforms can be fully correlated, similar to phased-array radars). Therefore, any desired covariance matrix can be achieved by using a very simple phased-array structure and space-time code in the transmitter. The main advantage of the proposed scheme is that it does not require diverse uncorrelated waveforms. This considerably reduces transmitter hardware and software complexity and cost. One the receiver side, multiple signals can be analyzed jointly in the time and space domains to improve the signal-to-interference-plus-noise ratio.

Measured and Predicted Durability and Mechanical Properties of Frozen-Thawed Fine Soils

Mohammad Vahdani,Mahmoud Ghazavi,Mahya Roustaei 대한토목학회 2020 KSCE JOURNAL OF CIVIL ENGINEERING Vol.24 No.3

An efficient experiment has been aimed in engineering fields for many years, which is provided through minimum number of tests and maximum amount of applicable results. Frozen soil is conceived to be an attractive subject for optimization processes. To reach an optimized design of experiment, a statistical method known as response surface method was used to largely reduce the number of tests and formulate a reasonable model for predicting the triaxial compressive strength and electrical resistivity. Considering the potential benefits of response surface method, a variety of effective factors including minimum freezing temperature during a cycle, number of freeze and thaw cycles and duration of freezing and/or thawing were investigated in order to have an overall outlook on the behavior of sandy lean clay subjected to different thermal regimes resembling natural conditions. In this study, triaxial compressive tests under confining pressures of 30 kPa and 90 kPa together with electrical resistivity tests were performed. In total, 38 treatments were performed under closed system to develop and verify models depending on mentioned factors, by which the mechanical behavior and durability of frozen soil could be reasonably estimated. The repeatability and relative errors of the derived models were also evaluated. It was shown that the derived statistical models were able to quantify the level of significance of each single input factor and their interactions with modeled properties, which can simplify the test protocol required to find the most destructive parameter and thermal regime. Minimum temperature and number of cycles were found to have the most significant effects on mechanical properties and durability, respectively.

Assessment of quality of life and its affecting factors in osteosarcopenic individuals in the Iranian older adult population: Bushehr Elderly Health (BEH) program

Amir Mohammad Vahdani,Mahnaz Sanjari,Noushin Fahimfar,Mahbube Ebrahimpur,Gita shafiee,Kazem Khalagi,Mohammad Javad Mansourzadeh,Iraj Nabipour,Bagher Larijani,Afshin Ostovar 대한골다공증학회 2023 Osteoporosis and Sarcopenia Vol.9 No.4

Objectives: This cross-sectional study, conducted as part of the Bushehr Elderly Health program stage II in Bushehr, Iran, aimed to evaluate health-related quality of life (HR-QoL) in individuals aged ≥ 60 with osteosarcopenia, a condition characterized by the co-occurrence of osteopenia/osteoporosis and sarcopenia. Given the increasing elderly population worldwide, understanding the HR-QoL of this demographic is crucial, with osteosarcopenia being a significant factor. Methods: The study enrolled 2369 participants aged ≥ 60 and collected demographic and anthropometric data. Various questionnaires, including the Short Form 12, Patient Health Questionnaire-9, Activities of Daily Living, and Instrumental Activities of Daily Living, were administered. Comparisons were made between individuals with and without osteosarcopenia. Regression models were employed to identify variables associated with HRQoL in those with osteosarcopenia. Results: Key findings revealed that 22.5% of participants had osteosarcopenia. Significantly different HR-QoL measures were observed between the 2 groups, especially in physical functioning and physical component summary scores. Male gender, advanced age, and chronic illnesses were linked to lower physical and mental HRQoL scores among those with osteosarcopenia. In female participants, a history of fractures and physical disability were associated with reduced quality of life. Conclusions: This study underscores the negative impact of osteosarcopenia on HR-QoL, particularly in male participants, with a focus on physical aspects. It also highlights age and chronic disease as contributing factors to diminished HR-QoL in individuals with osteosarcopenia. These findings emphasize the importance of addressing osteosarcopenia in the elderly population to improve their overall well-being.

Evolutionary-base finite element model updating and damage detection using modal testing results

Mehdi Vahidi,Shahram Vahdani,Aicha Remil,Nima Jamshidi,Alireza Taghavee Kanee 국제구조공학회 2019 Structural Engineering and Mechanics, An Int'l Jou Vol.70 No.3

This research focuses on finite element model updating and damage assessment of structures at element level based on global nondestructive test results. For this purpose, an optimization system is generated to minimize the structural dynamic parameters discrepancies between numerical and experimental models. Objective functions are selected based on the square of Euclidean norm error of vibration frequencies and modal assurance criterion of mode shapes. In order to update the finite element model and detect local damages within the structural members, modern optimization techniques is implemented according to the evolutionary algorithms to meet the global optimized solution. Using a simulated numerical example, application of genetic algorithm (GA), particle swarm (PSO) and artificial bee colony (ABC) algorithms are investigated in FE model updating and damage detection problems to consider their accuracy and convergence characteristics. Then, a hybrid multi stage optimization method is presented merging advantages of PSO and ABC methods in finding damage location and extent. The efficiency of the methods have been examined using two simulated numerical examples, a laboratory dynamic test and a high-rise building field ambient vibration test results. The implemented evolutionary updating methods show successful results in accuracy and speed considering the incomplete and noisy experimental measured data.

Nonlinear finite element modeling of the self-centering steel moment connection with cushion flexural damper

Ali Nazeria,Reza Vahdani,Mohammad Ali Kafi 국제구조공학회 2023 Structural Engineering and Mechanics, An Int'l Jou Vol.87 No.2

The latest earthquake’s costly repairs and economic disruption were brought on by excessive residual drift. Selfcentering systems are one of the most efficient ways in the current generation of seismic resistance system to get rid of and reduce residual drift. The mechanics and behavior of the self-centering system in response to seismic forces were impacted by a number of important factors. The amount of post-tensioning (PT) force, which is often employed for the standing posture after an earthquake, is the first important component. The energy dissipater element is another one that has a significant impact on how the self-centering system behaves. Using the damper as a replaceable and affordable tool and fuse in self-centering frames has been recommended to boost energy absorption and dampening of structural systems during earthquakes. In this research, the self-centering steel moment frame connections are equipped with cushion flexural dampers (CFDs) as an energy dissipator system to increase energy absorption, post-yielding stiffness, and ease replacement after an earthquake. Also, it has been carefully considered how to reduce permanent deformations in the self-centering steel moment frames exposed to seismic loads while maintaining adequate stiffness, strength, and ductility. After confirming the FE model’s findings with an earlier experimental PT connection, the behavior of the self-centering connection using CFD has been surveyed in this study. The FE modeling takes into account strands preloading as well as geometric and material nonlinearities. In addition to contact and sliding phenomena, gap opening and closing actions are included in the models. According to the findings, self-centering moment-resisting frames (SF-MRF) combined with CFD enhance post-yielding stiffness and energy absorption with the least amount of permeant deformation in a certain CFD thickness. The obtained findings demonstrate that the effective energy dissipation ratio (β), is increased to 0.25% while also lowering the residual drift to less than 0.5%. Also, this enhancement in the self-centering connection with CFD’s seismic performance was attained with a respectable moment capacity to beam plastic moment capacity ratio.

Nonlinear optical properties of a hydrogenic impurity in an ellipsoidal finite potential quantum dot

G. Rezaei,M.R.K. Vahdani,B. Vaseghi 한국물리학회 2011 Current Applied Physics Vol.11 No.2

The linear and the third-order nonlinear optical absorption coefficient and refractive index changes of a hydrogenic impurity in an ellipsoidal quantum dot have been investigated, using the compact-density matrix formalism and an iterative method. In this regard, the effect of the size and geometry of the dot,aluminium concentration in GaAs/Al_xGa_1-x_As structures, and optical intensity on the optical absorption coefficient and refractive index changes are investigated. It is found that the light intensity, size and geometry of the dot and aluminium concentration have a great influence on the absorption coefficient and refractive index changes of the dot.