Squeeze Film Effect in Surface Micromachined Nano Ultrasonic Sensor for Different Diaphragm Displacement Profiles.

In the present paper, we have analytically explored the small variations of the local pressure in the trapped air film of both sides of the clamped circular capacitive micromachined ultrasonic transducer (CMUT), which consists of a thin movable membrane of silicon nitride (Si3N4). This time-independent pressure profile has been investigated thoroughly by solving the associated linear Reynold's equation in the framework of three analytical models, viz. membrane model, plate model, and non-local plate model. The solution involves Bessel functions of the first kind. The Landau-Lifschitz fringing technique has been assimilated to engrave the edge effects in estimation of the capacitance of CMUT, which should be considered in the micrometer or lesser dimension. To divulge the dimension-based efficacy of the considered analytical models, various statistical methods have been employed. Our use of contour plots of absolute quadratic deviation revealed a very satisfactory solution in this direction. Though the analytical expression of the pressure profile is very cumbersome in various models, the analysis of these outputs exhibits that the pressure profile follows the displacement profile in all the cases indicating no viscous damping. A finite element model (FEM) has been used to validate the systematic analyses of displacement profiles for several radii and thicknesses of the CMUT's diaphragm. The FEM result is further corroborated by published experimental results bearing excellent outcome.

Theoretical Study of ZnS Monolayer Adsorption Behavior for CO and HF Gas Molecules.

Adsorption of carbon monoxide (CO) and hydrogen fluoride (HF) gas molecules on a ZnS monolayer with weak van der Waals interactions is studied using the DFT + U method. From our calculation, the ZnS monolayer shows chemisorption with CO (E ads = -0.96 eV) and HF (E ads = -0.86 eV) gas molecules. Bader charge analysis shows that charge transfer is independent of the binding environment. A higher energy barrier for CO when migrating from one optimal site to another suggests that clustering may be avoided by the introduction of multiple CO molecules upon ZnS, while the diffusion energy barrier (DEB) for HF suggests that binding may occur more easily for HF gas upon the ZnS ML. Adsorption of the considered diatomic molecule also results in a significant variation in effective mass and therefore can be used to enhance the carrier mobility of the ZnS ML. Additionally, the calculation of recovery time shows that desirable sensing and desorption performance for CO and HF gas molecules can be achieved at room temperature (300 K).

Evaluation of radiation doses at diagnostic X-ray control panels and outside patient entrance doors in Aizawl district, India.

The purpose of this research was to measure the radiation level and estimate the dosage at the control panel (CP) and outside the patient entrance door (PED) of diagnostic X-ray installations. This is important for ensuring the safety of workers and the public, particularly in the study area, where there is no proper radiation monitoring service. A water phantom, 10-L fresh water in a plastic container, was used as the source of scattered radiation. Using an ion-chamber survey meter, the stray radiation rate was measured at the CP and outside the PED for both chest and couch missions. The CPs were fully covered by a protective barrier, providing a negligible exposure rate (i.e., 0.07-4.2 mR/h for chest and 0.21-3.8 mR/h for couch). By contrast, installations that did not properly cover the CP showed relatively high exposures (from 18 to 205 mR/h for chest and 2.4-270 mR/h for couch). The radiation rates outside the PED in installations having lead-lined doors were negligibly low; whereas, in installations having no lead-lining, exposure rates reached as high as 95 and 110 mR/h for chest and couch missions, respectively. The occupational doses were well below the Atomic Energy Regulatory Board dose limit (i.e., 40 mR/week). However, excessive doses were observed in public spaces outside the PED, compared with the dose limit for the public (i.e., 2 mR/week).

Qualitative study of mechanical parameters of conventional diagnostic X-ray machines in Mizoram.

The present study examined the mechanical attributes of 135 conventional diagnostic X-ray machines in Mizoram, India. The purpose of studying the X-ray mechanical parameters, such as congruency, perpendicularity of the central beam, and half-value layer, was to improve the quality of the diagnostic image and reduce the patient dose. A battery-operated portable dosimeter was used to measure output radiation of the X-ray machine. The half-value layer was measured at a constant accelerating potential of 70 kVp and tube load. To measure the congruency and beam alignment perpendicularity, a congruence and alignment tool was used. The survey data were collected between June 2015 and June 2016. The authors followed international standard test procedures, and the results were compared to national and international standards. SPSS Statistics for Windows, Version 17 was used to calculate the mean, range, and standard deviation. The half-value layer ranged from 0.45 to 3.00 mm; the mean half-value layer was 1.60 ± 0.51 SD mm. In comparison with national and international standards, only 27.83% (national) and 15.64% (international) of the machines' filtration were found to be within acceptable limits. The congruence misalignment of the x-axis varied between 0.50% and 15.30% of the source-to-image distance; for the y-axis, it ranged from 0.50 to 10.90%. When the congruence between the radiation beam and optical field was tested, 80.85% of diagnostic X-ray machines did not meet the prescribed acceptance parameters. When the perpendicularity between the central beam and the image receptor was tested, 69.81% did not meet safety standards.

Variations of soil radon concentrations along Chite fault in Aizawl district, Mizoram, India.

The present study concerns measurements of radon emissions from soil carried out during March to July 2013 at Chite fault in Aizawl district, Mizoram, India. In this study, continuous radon monitoring in soil was done by using LR-115 type II nuclear track detector (Kodak-Pathe, France make), and the exposed films were replaced weekly. A negative correlation coefficient (-0.47) between radon concentration and barometric pressure was found during the investigation period. The average radon concentration was observed to be 1785.71 Bq m(-3) with a standard deviation of 633.07 Bq m(-3). The maximum and minimum values of radon concentration during this period were found to be 3693.88 and 904.76 Bq m(-3), respectively. An anomalous increase in radon concentration was observed on 112th day (i.e. on 14 June 2013) during the investigation period just 1 d prior to the event of M 3.5, which occurred within 120-km distance from the monitoring site.