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Naveed Ullah,박상준,이영중,정연욱,박소연 한국물리학회 2015 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.67 No.4
Quartz tuning forks (QTFs) are being more frequently adopted instead of micromachined cantilevers as force sensors in scanning probe microscopes due to their mechanical stability, high quality factors, and wide availability at low costs. Mass-produced QTFs are typically housed in vacuumsealed canisters, and this necessitates the removal of the vacuum canisters to make necessary modifications such as attaching a tip or an optical fiber. Commonly, the decrease in the quality factor after the removal of the canister is attributed to an increase in air damping with no further investigation of other possible causes. We carried out several experiments with QTFs before and after the canisters were removed. Despite a vacuum level below 10−5 Torr, all investigated QTFs exhibited decreased quality factors once the protective canisters had been removed. We present possible causes for this observation by analyzing optical microscope images. Also, complete mechanical and electrical characterizations of the QTFs are presented, taking advantage of the analogies that exist between mechanical and electrical systems.
Naveed ULLAH,박상준,이영중,박소연 한국물리학회 2015 새물리 Vol.65 No.1
Quartz tuning forks (QTFs) have been used as alternative force detection sensors in scanning probe microscopy due to their many favorable properties such as high quality factor, low cost, excellent mechanical stability, and wide availability. A QTF is usually modeled by using the Butterworth-Van Dyke equivalent circuit, and the relevant electrical parameters associated with the Butterworth-Van Dyke equivalent circuit can be calculated by analyzing the complex admittance measured with an impedance analyzer. However, an impedance analyzer is not a commonlyavailable laboratory instrument due to its high cost. It is also employed in radio-frequency (RF) and microwave measurements where the operating frequencies are outside the range of interest. Because the frequency range of interest for QTFs is usually less than 100 kHz, a relatively low-frequency impedance measurement setup involving a basic preamplifier and a lock-in amplifier can effectively replace an impedance analyzer. We present our implementation of such a setup and the measured electrical parameters. In addition, the measurement results obtained by using our low-frequency lock-in amplifier setup and those obtained by using a commercial precision impedance analyzer are compared to validate our approach.
Ullah, Muhammad Zia,Khan, Ashraf Ullah,Afridi, Ruqayya,Rasheed, Hina,Khalid, Sidra,Naveed, Muhammad,Ali, Hussain,Kim, Yeong Shik,Khan, Salman Elsevier 2018 INTERNATIONAL IMMUNOPHARMACOLOGY Vol.61 No.-
<P><B>Abstract</B></P> <P>In the current study, the puerarin was investigated for both acute Carrageenan and chronic CFA-induced inflammatory pain models. The Puerarin treatment significantly attenuated (P < 0.001) the mechanical hyperalgesia and mechanical allodynia in both Carrageenan and CFA-induced hyperalgesia. The Puerarin treatment also remarkably reduced (<I>p</I> < 0.001) the thermal hyperalgesic responses in both acute Carrageenan as well as chronic CFA-induced models. Furthermore, the Puerarin administration was also associated with significant inhibition of (<I>p</I> < 0.001) paw edema in both Carrageenan and CFA-induced models. The inflammatory mediators such as IL-1β, IL-6, TNF-α and vascular endothelial growth factor (VEGF) are significantly enhanced during inflammatory conditions, however, the Puerarin administration significantly altered (P < 0.001) the mRNA expression levels of these mediators. Additionally, the Puerarin treatment also significantly enhanced (P < 0.001) the mRNA expressions levels of the anti-oxidant enzymes such as Nrf2, HO-1 and SOD2. The Puerarin treatment is associated with significant (P < 0.001) inhibition of the acetic acid-induced Evans blue vascular permeability. Moreover, the concentration of Puerarin in various tissues was analyzed using High-performance liquid chromatography (HPLC) and the results showed that the Puerarin was significantly distributed towards the peripheral tissues such as liver and kidney and less distributed towards the brain.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Puerarin possess strong antinociceptive properties in animal models. </LI> <LI> Puerarin inhibited various inflammatory cytokines (IL-1β, IL-6, TNF-α), and (VEGF). </LI> <LI> Vascular permeability was significant inhibited by puerarin. </LI> <LI> No apparent toxic effect of puerarin was observed. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Microchannel gas cooler simulation for transcritical CO2 cycle in automotive A/C systems
Naveed Ullah,Shehryar Ishaque,Man-Hoe Kim 대한설비공학회 2022 대한설비공학회 학술발표대회논문집 Vol.2022 No.11
This study aims to develop a microchannel gas cooler model for evaluating the performance of a transcritical CO₂ mobile air-conditioning system. A simulation model is developed using segment-by-segment approach in the MATLAB platform. The simulations are performed under different operating conditions and results are validated against the experimental data. Effect of different operating conditions including air and refrigerant inlet temperatures, flow rates, air velocity, and operating pressure on the gas cooler performance is studied. Results showed that the gas cooler capacity and refrigerant-side pressure drop are in good agreement with the experimental data within 4.29% and 8.88%, respectively.
Sajid Ullah Butt,Mamoona Arshad,Aamer Ahmed Baqai,Hasan Aftab Saeed,Naveed Akmal Din,Rehan Ahmed Khan 한국정밀공학회 2021 International Journal of Precision Engineering and Vol.22 No.5
Fixture design is one of the main factors which affect the final product quality. Proper design of fixture plays an important role in ensuring the required tolerance of the product. Proper placement of locators is one of the prominent factors in fixture design. Locators are elastic: they deform under clamping and machining forces causing rigid body displacement of the workpiece which in turn affects the part quality. In this article, a 3-2-1 type of fixturing system having elastic locators around a considerably rigid rectangular workpiece is considered. A genetic algorithm is proposed, which uses a fitness function that evaluates the positioning error of the workpiece under external forces and torque. Among several variables, 12 variables, which define the placement of locators, are chosen to be optimized while minimizing the positioning error of the workpiece at the point of action of machining force. The proposed algorithm optimizes the 12 interlinked variables, within the specified region, for machining force and torque at a single point. However, when the cutting tool moves to any other point on the workpiece, it is observed that either the workpiece loses its contact with any one of the locators or the positioning error increases by a large value. To overcome this issue, the proposed algorithm is further modified for placement optimization to cater for multi-point machining, and the isostatism of the workpiece is ensured by checking the magnitude and direction of displacement (of what?) at each point of workpiece-locator contact. Finally, the original and modified GA algorithms are explained through a case study where the single point optimized placement shows loss of contact when machining force is applied at other points. The placement optimized from the modified algorithm shows that the isostatism of the workpiece remains intact while all four positioning errors are converged towards the same value. The results obtained from the proposed and modified algorithm are verified using ANSYS simulation.
Shehryar Ishaque,Naveed Ullah,Man-Hoe Kim 대한설비공학회 2022 대한설비공학회 학술발표대회논문집 Vol.2022 No.11
This study presents a parametric optimization of a microchannel gas cooler for a transcritical CO₂ mobile air-conditioning system. One of the main difficulties in selecting effective microchannel gas coolers for mobile air-conditioning systems is taking into account size, weight, and available space. One-dimensional, two-dimensional, or three-dimensional spatial restrictions are possible (i.e. the combination of length, height, and width). The height of the core is associated with the number of tubes, while the width of the core is associated with the number of ports. To study the simultaneous effect of a number of tubes, the number of ports in each tube, and tube length, different combinations were selected within the practical range to get an optimal dimension while keeping the total core volume constant. An optimal solution can be selected based on the maximum gas cooler capacity, minimum pressure drop, or the ratio of gas cooler capacity to pressure drop. One of the major concerns in the mobile air-conditioning system is a space limitation. Therefore, the current study focuses on the parametric optimization of a microchannel gas cooler based on the maximum heat exchanger capacity or minimum pressure drop concerning the available size and space.
Re: Comments on “Chorea as a Presentation of SARS-CoV-2 Encephalitis: A Clinical Case Report”
Muhammad Hassan,Naveed Ullah Khan,Mazhar Badshah 대한파킨슨병및이상운동질환학회 2022 Journal Of Movement Disorders Vol.15 No.1
There are various etiologies and pathogenesis of myoclonus, most often categorized into cortical, subcortical, or spinal myoclonus. However, the pathophysiology of chorea is mainly implicated in dysfunction of the basal ganglia motor circuitry.