Channel Scanning and Access Point Selection Mechanisms for 802.11 Handoff: A Survey

While the cellular technology has been evolving continuously in recent years and client handoffs remain unnoticed, the 802.11 networks still impose an enormous latency issue once the client device decides to roam between the Access Point (AP). This latency is caused by many factors reckoning on scanning the channels and searching for APs with better signal strength. Once data from all the nearby APs has been collected, the client picks the most suitable AP and tries to connect with it. The AP verifies if it has enough capability to serve the client. It also ensures that the client has the required parameters and supported rates to match with the AP. The AP then processes this request, generates a new Association ID and sends it back to the client, thereby granting access to connect. Throughout this re-association process, the client fails to receive or send any data frames and experiences a lag between leaving the old and associating with a new AP. Originally, 802.11 authentication frames were designed for Wired Equivalent Privacy protocol, but later it was found to be insecure and thus got depreciated. Keeping these security aspects concerning shared key authentication in mind, few additional drafts were introduced by IEEE that concerned many key exchanges between the devices. IEEE 802.11r was introduced in 2008 that permits wireless clients to perform faster handoff along with additional data security standards. The key exchange method was redefined and also the new security negotiation protocol started serving wireless devices with a better approach. This enables a client to set up the Quality of Service state and security on an alternative AP before making a transition which ends up in minimal connectivity losses. Although this was an excellent step towards minimizing the service disruption and channel scanning, failure to remain connected with consecutive suitable APs within the minimum time continued to be a challenge. Different manufacturers use their custom-built methodology of handling a client handoff and hence the latency costs differ based on the type of handoff scheme deployed on the device. This thesis focuses on the foremost economical researches throughout recent years which targets minimizing the delays involved with channel scanning and AP selection. A wide sort of enhancements, whether it is on a client device or the AP, has been discussed and compared. Some modifications are associated with enhancing channel scan period or using beacons, and probe requests/responses in an efficient manner. Others concentrate on modifying the device hardware configuration and switching between Network Interfaces. Central controllers are a solution to handoff delays that may track the status of each device within the network and guide them to provide the appropriate Quality of Service to the end-users

Effect of Different Additives on Cloud Point of Non Ionic Surfactant

Determination of cloud point of non-ionic surfactants have wide applications as it is the temperature where the mixture starts to phase separate and the two phases appear, thus becoming cloudy. Non-ionic surfactants find suitable applications for recovery of membrane components under mild non-denaturing condition. Knowing the cloud point helps us to determine the storage stability since storing formulations at temperatures significantly higher than the cloud point may result in phase separation and instability. Generally, non-ionic surfactants show optimal effectiveness when used near or below their cloud point. In this present work, effects of different additives on cloud point of non-ionic surfactants have been studied. Triton X-100 (TX-100) has been used as the non-ionic surfactant and observations have been done subsequently for different concentration of TX-100 by taking various additives like NaCl, Na2SO4, CaCl2 and corresponding temperature were noted down. Other than non-ionic surfactants, experiments were conducted for both cationic as well as anionic surfactants. Based upon the result, graphs were plotted which comply well with the theoretical study

Particulate Matter and Human Health

This chapter provides an introduction to particulate matter by discussing various ways of categorisation, characterisation and their health effects. The natural and anthropogenic sources of atmospheric particulate matter are discussed. The chapter also introduces qualitatively some aerosol concepts, such as their chemical composition and size distribution. Some examples are provided to illustrate how particulate matter, despite being microscopic particles, can manifest themselves in the atmosphere. Finally, the various pathways by which particulate matter impacts the health system are reviewed along with their interactions to understand concept behind the PM-associated health effects

A CROSS-SECTIONAL STUDY TO ESTIMATE THE PREVALENCE OF HYPERTENSION IN URBAN FIELD PRACTICE AREA OF MEDICAL COLLEGE IN METROPOLITAN CITY OF INDIA

Objectives: The objectives of the study were to estimate the prevalence of hypertension in people above 35 years and to study the sociodemographic profile of the study subjects. Methods: The study was a cross-sectional study conducted in urban field practice area of medical college. Five chawls were selected by simple random sampling out of 42 chawls. Males and females above 35 years of age living in study area formed a sample frame. Sample size was calculated and it was 667. As per the protocol, informed written consent and demographic details with clinical data were obtained from the patients. Results: A total of 667 participants were included from five chawls. Maximum number of participants, that is, 37%; were from the age group of 35 to 44, consisting of 41% males and 59% females. Around 67% of study respondents belonged to the age group of 35–54 years. Around 3/4th of study respondents had studied up to primary school and secondary and high school. Out of 263 males, 37%, that is, 98 respondents were hypertensive, and out of 404 females, 152, that is, 38% were hypertensive. Hence, the total prevalence of hypertension in this study was 37.5%. Conclusion: Hypertension is the new era pandemic which is the leading cause of morbidity and mortality in the world and is ranked third as a cause of disability-adjusted life years. To control hypertension, it is imperative to identify and modify its risk factors

Further evidence that a terminal drought tolerance QTL is also associated with reduced salt uptake

AbstractEarlier, we established that a major drought tolerance QTL on linkage group 2 of pearl millet is also associated with reduced salt uptake and enhanced growth under salt stress. Present study was undertaken to re-assess the performance of drought tolerant (PRLT 2/89-33) and drought sensitive (H 77/833-2) parents along with two QTL-NILs (ICMR 01029 and ICMR 01040), under salinity stress specifically imposed during post-flowering growth stages when plants had developed their ion sinks in full. Time course changes in ionic accumulation and their compartmentalization in different plant parts was studied, specifically to monitor and capture changes conferred by the two alleles at this QTL, at small intervals. Amongst different plant parts, higher accumulation of toxic ion Na+ was recorded in roots. Further, the Na+ concentration in roots of the testcross hybrid of the drought-sensitive parent (H 77/833-2) reached its maximum at ECiw 15dSm−1 within 24h after salinity imposition, whereas it continued to increase with time in the testcross hybrids of the drought tolerant parent PRLT 2/89-33 as well as those of its QTL-NILs (ICMR 01029 and ICMR 01004) and reached at its maximum at 120h stage. Comparison of differential distribution of toxic ions in individual leaves revealed that Na+ ions were not uniformly distributed in the leaves of the drought-tolerant parent and drought-tolerant QTL-NILs; but accumulated preferentially in the older leaves, whereas the hybrid of the drought-sensitive parent showed significantly higher Na+ concentration in all main stem leaves irrespective of their age. Dynamics of chlorophyll and proline concentration variation studied under salt stress at late flowering stages revealed a greater reduction, almost twice, in both leaf chlorophyll and proline concentrations in younger leaves in the hybrids of the sensitive parent as compared to the tolerant parent and QTL NILs. Imposition of salinity stress even at flowering stage affected the yield performance in pearl millet, wherein higher yield was recorded in drought tolerant parent and the two QTL-NILs compared to drought sensitive parent

Simulation of Field Oriented Control Variable Frequency Induction Motor Drive

now days replacing the DC motor with Induction motors are requirement of each plant due to very high operating cost associated with DC motors. To achieve the better dynamic response like as DC motors IM drives are developed. Field Oriented Control based drives with pulse width modulation technique for operation of inverter. In field oriented control method whole induction motor is converted into mathematical DC motor model and control like a dc motor. by Feedback control loop system a gate pulse is generated for the pulse width modulated inverter and according to that voltage and frequency to be controlled. These new technique improve the torque speed characteristics and reduced the response time. This results a very good speed controlling of induction motor and required speed torque characteristic