Query: tahmid hassan talukdar

title: Nanoimprinting of Refractive Index: Patterning Subwavelength Effective Media for Flat Optics
abstract: Subwavelength effective media offer a powerful tool for tailoring optical properties on the surface of a chip but remain challenging to realize at optical frequencies owing to their demand for nano.

title: Status of thermal comfort in naturally ventilated university classrooms of Bangladesh in hot and humid summer season
abstract: Indoor thermal comfort is dynamic because of complex interactions between occupants, season specific climatic parameters, and region specific socio cultural setup. A thermally comfortable environment is a key requirement for obtaining good classroom performance. Providing adequate thermal comfort is considered to be the greatest challenge in naturally ventilated (NV) conditions in tropical cities during the summer season. Present study is focused on assessing student's thermal perceptions and behavioural adjustment in NV university classrooms within the tropical wet climatic zone in Bangladesh. Field surveys consisting of 24 observations were made during the peak summer in 2017, and 579 data sets were collected and analyzed. The mean indoor air temperature, relative humidity, and wind velocity were observed at 30.9 degC, 78.4% and 0.8 m/s. We used a linear regression model to estimate the neutral temperature, but Griffiths predicted mean comfort temperature (27.8 degC) was found to be more relevant to the classroom environment and the sample size. About 43.7% of Students voted within two central comfort bands (0 and 1) on the ASHRAE thermal sensation scale having a temperature range of 27.5 33.8 degC. Hence, we compared student comfort temperatures (Tcomf) obtained from Griffiths method with the existing thermal comfort models. About 87.7% and 81% of students Tcomf was observed within 80% and 90% acceptability zone of ASHRAE standard 55 respectively. Moreover, about 89.3% and 95.9% of the students' Tcomf was found within Category II and Category III comfort bands of CEN (EN 15251) respectively. Results indicate that students are comfortably adapted to the extreme weather during summer.

title: Multifunctional focusing and accelerating of light with a simple flat lens.
abstract: The wavefronts emerging from phase gradient metasurfaces are typically sensitive to incident beam properties such as angle, wavelength, or polarization. While this sensitivity can result in undesired wavefront aberrations, it can also be exploited to construct multifunctional devices which dynamically vary their behavior in response to tuning a specified degree of freedom. Here, we show how incident beam tilt in a one dimensional metalens naturally offers a means for changing functionality between diffraction limited focusing and the generation of non paraxial accelerating light beams. This attractively offers enhanced control over accelerating beam characteristics in a simple and compact form factor.

title: Hyperchromatic structural color for perceptually enhanced sensing by the naked eye
abstract: Modern scientific instrumentation and sensors are often bulky, expensive, and/or cumbersome to operate. Colorimetric sensors on the other hand offer a promising solution to these problems, as they can be analyzed with high spatiotemporal resolution by digital cameras or the naked eye. However, the performance of colorimetric sensors is typically inferior to the bulky/expensive alternatives as it can be difficult to convert small input stimulus variations into a large color response. This work introduces a means to address and overcome this problem and opens the door to types of high performance colorimetric sensors, which are competitive with and/or offer greater functionality than the bulky/expensive alternatives. Colorimetric sensors offer the prospect for on demand sensing diagnostics in simple and low cost form factors, enabling rapid spatiotemporal inspection by digital cameras or the naked eye. However, realizing strong dynamic color variations in response to small changes in sample properties has remained a considerable challenge, which is often pursued through the use of highly responsive materials under broadband illumination. In this work, we demonstrate a general colorimetric sensing technique that overcomes the performance limitations of existing chromatic and luminance based sensing techniques. Our approach combines structural color optical filters as sensing elements alongside a multichromatic laser illuminant. We experimentally demonstrate our approach in the context of label free biosensing and achieve ultrasensitive and perceptually enhanced chromatic color changes in response to refractive index changes and small molecule surface attachment. Using structurally enabled chromaticity variations, the human eye is able to resolve ~0.1 nm spectral shifts with low quality factor (e.g. Q 15) structural filters. This enables spatially resolved biosensing in large area (approximately centimeters squared) lithography free sensing films with a naked eye limit of detection of ~3 pg/mm2, lower than industry standard sensors based on surface plasmon resonance that require spectral or angular interrogation. This work highlights the key roles played by both the choice of illuminant and design of structural color filter, and it offers a promising pathway for colorimetric devices to meet the strong demand for high performance, rapid, and portable (or point of care) diagnostic sensors in applications spanning from biomedicine to environmental/structural monitoring.

title: Ultra Sensitive and High Figure of Merit Interferometric Biosensors using Dispersion Effects in Porous Waveguides
abstract: We report an interferometric biosensor that theoretically and experimentally exceeds the sensitivity predicted by bulk effective medium theory. The devices are realized by engineering dispersion effects in high confinement factor multilayer porous silicon rib waveguides.

title: Performance Improvements of AODV by Black Hole Attack Detection Using IDS and Digital Signature
abstract: Department of Information and Communication Technology (ICT) Comilla University, Cumilla, Bangladesh Centre for Cyber Security, Faculty of Information Science and Technology, Universiti Kebangsaan Malaysia (UKM) 43600 UKM Bangi, Selangor, Malaysia Department of Computer Science and Information Technology, Maulana Azad National Urdu University, Hyderabad, India Computing Department, Engineering Faculty, Global College of Engineering and Technology, Oman

title: IoT Based Medical Assistant for Efficient Monitoring of Patients in Response to COVID 19
abstract: We have developed a complete model of monitoring patients at regular intervals through an interconnected network among the doctors, nurses and patients with a view to minimizing the workload of the doctors and nurses, reducing the chances of medical professionals being infected by COVID 19 type of contagious disease and increasing the overall efficiency of patient monitoring in hospitals. Bio medical sensors interfaced with microcontroller are used to collect the data of heart beat rate, body temperature and body movement to get an overview of the present health condition of the patient. The recorded data are stored in an excel file and updated automatically to the internet via OneDrive in every 30 seconds. In case of any large deviation from the normal condition, an automated alarm system will notify the assigned doctor about the condition of the patient. A medication reminder system is added in our designed android app to notify the patient to take the medicine prescribed by the doctor at proper time. The patient can also call the nurse in case of emergency and there is also scope for the patient to control the position of the bed according to his comfort. The level of saline or blood injected into the vein of the patient can also be monitored in our system to inform the nurse at the time of being finished.

title: Prediction of Epidemics Trend of COVID 19 in Bangladesh
abstract: Amid a critical and emergent situation like the coronavirus disease (COVID 19) pandemic related to extreme health and economic repercussions, we used and presented the mathematical modeling like susceptible infectious recovered (SIR) to have a numerical demonstration that can shed light to decide the fate of the scourge in Bangladesh. To describe the idea about the factors influencing the outbreak data, we presented the current situation of the COVID 19 outbreak with graphical trends.  Primary data were collected and analyzed by using a pre created Google Survey form having a pre set questionnaire on the social distancing status of different districts. Secondary data on the total and the daily number of laboratory tests, confirmed positive cases, and death cases were extracted from the publicly available sources to make predictions. We estimated the basic reproduction number (R* based on the SIR mathematical model and predicted the probable fate of this pandemic in Bangladesh.  Quarantine situations in different regions of Bangladesh were evaluated and presented. We also provided tentative forecasts until 31 May 2020 and found that the predicted curve followed the actual curve approximately. Estimated R* values (6.924) indicated that infection rate would be greater than the recovery rate. Furthermore, by calibrating the parameters of the SIR model to fit the reported data, we assume the ultimate ending of the pandemic in Bangladesh by December 2022.  We hope that the results of our analysis could contribute to the elucidation of critical aspects of this outbreak and help the concerned authority toward decision making.

title: Single mode porous silicon waveguide interferometers with unity confinement factors for ultra sensitive surface adlayer sensing.
abstract: Guided wave optics has emerged as a promising platform for label free biosensing. However, device sensitivity toward surface bound small molecules is directly limited by the evanescent interaction and low confinement factor with the active sensing region. Here, we report a mesoporous silicon waveguide design and inverse fabrication technique that resolves the evanescent field interaction limitation while achieving maximal transverse confinement factors and preserving single mode operation. The waveguide sensors are characterized in a Fabry Perot interferometer configuration and the ultra high sensitivity to small molecule adlayers is demonstrated. We also identify dispersion to be a promising degree of freedom for exceeding the sensitivity limits predicted by the conventional non dispersive effective medium theory.

title: Patterning Refractive Index on the Surface of a Chip by Direct Nanoimprinting
abstract: We demonstrate a means for patterning refractive index on the surface of a chip by directly imprinting porous nanomaterials. This offers a new route toward high index contrast and low cost chip scale diffractive, waveguided and meta optic devices.