Throughput Analysis of Primary and Secondary Networks in a Shared IEEE 802.11 System

In this paper, we analyze the coexistence of a primary and a secondary (cognitive) network when both networks use the IEEE 802.11 based distributed coordination function for medium access control. Specifically, we consider the problem of channel capture by a secondary network that uses spectrum sensing to determine the availability of the channel, and its impact on the primary throughput. We integrate the notion of transmission slots in Bianchi's Markov model with the physical time slots, to derive the transmission probability of the secondary network as a function of its scan duration. This is used to obtain analytical expressions for the throughput achievable by the primary and secondary networks. Our analysis considers both saturated and unsaturated networks. By performing a numerical search, the secondary network parameters are selected to maximize its throughput for a given level of protection of the primary network throughput. The theoretical expressions are validated using extensive simulations carried out in the Network Simulator 2. Our results provide critical insights into the performance and robustness of different schemes for medium access by the secondary network. In particular, we find that the channel captures by the secondary network does not significantly impact the primary throughput, and that simply increasing the secondary contention window size is only marginally inferior to silent-period based methods in terms of its throughput performance.Comment: To appear in IEEE Transactions on Wireless Communication

The 60 GHz IMPATT diode development

The objective is to develop 60 GHz IMPATT diodes suitable for communications applications. The performance goals of the 60 GHz IMPATT is 1W CW output power with a conversion efficiency of 15 percent and 10-year lifetime. The final design of the 60 GHz IMPATT structure evolved from computer simulations performed at the University of Michigan. The initial doping profile, involving a hybrid double-drift (HDD) design, was derived from a drift-diffusion model that used the static velocity-field characteristics for GaAs. Unfortunately, the model did not consider the effects of velocity undershoot and delay of the avalanche process due to energy relaxation. Consequently, the initial devices were oscillating at a much lower frequency than anticipated. With a revised simulation program that included the two effects given above, a second HDD profile was generated and was used as a basis for fabrication efforts. In the area of device fabrication, significant progress was made in epitaxial growth and characterization, wafer processing, and die assembly. The organo-metallic chemical vapor deposition (OMCVD) was used. Starting with a baseline X-Band IMPATT technology, appropriate processing steps were modified to satisfy the device requirements at V-Band. In terms of efficiency and reliability, the device requirements dictate a reduction in its series resistance and thermal resistance values. Qualitatively, researchers were able to reduce the diodes' series resistance by reducing the thickness of the N+ GaAs substrate used in its fabrication

ANALYTICAL METHOD DEVELOPMENT AND VALIDATION OF NADIFLOXACIN BY HIGH PERFORMANCE LIQUID CHROMATOGRAPHY

Objective: In the present work, a rapid, precise and sensitive HPLC Method with UV detection (237 nm) for analysis of Nadifloxacin in Bulk was developed. Methods: Chromatography was performed with a mobile phase containing a mixture of 0.05 %v/v trifluoro acetic acid and acetonitrile (65:35 v/v) with flow rate 1.2 ml min-l. The proposed method was validated as per the standard guidelines. Result: The retention time was found to be 12.3 min. In the range of 0.03-5 ppm, the linearity of Nadifloxacin shows a correlation co-efficient of 0.9997. Percentage recovery of the drug was found to be good (98-102%). Validation of the developed method was successful for precision, robustness, specificity and selectivity and ruggedness. Conclusion: The developed HPLC method was found to be simple, sensitive, precise, accurate and reproducible and can be successfully used for the quantitative estimation of Nadifloxacin in bulk

Missile Longitudinal Dynamics Control Design Using Pole Placement and LQR Methods

In high-maneuvering missile systems, with severe restrictions on actuator energy requirements, it is desirable to achieve the required performance with least actuation effort. Linear Quadratic Regulator (LQR) has been in literature for long and has proven it’s mettle as an optimal controller in many benign aerospace applications and industrial applications where the response times of the plant, in most cases, are seen to be greater than 10 seconds. It can be observed in the literature that LQR control methodology has not been explored enough in the tactical missile applications where requirement of very fast airframe response times are desired, typically of the order of milliseconds. In the present research, the applicability of LQR method for one such agile missile control has been critically explored. In the present research work, longitudinal dynamic model of an agile missile flying at high angle of attack regime has been established and an optimal LQR control solution has been proposed to bring out the required performance demanding least control actuator energy. A novel scheme has been presented to further optimise the control effort, which is essential in this class of missile systems with space and energy constraints, by iteratively computing optimal magnitude state weighing matrix Q and control cost matrix R. Pole placement design techniques, though extensively used in aerospace industry because of ease of implementation and proven results, do not address optimality of the system performance. Hence, a comparative study has been carried out to verify the results of LQR against pole placement technique based controller. The efficacy of LQR based controller over pole placement design techniques is successfully established with minimum control energy requirement in this paper. Futuristic high maneuvering, agile missile control design with severe space and energy constraints stand to benefit incorporating the controller design scheme proposed in this paper.&nbsp

Occupant protection in far-side impacts

The potential injury reducing benefits by a far-side airbag was evaluated by means of human body modelling (HBM). The human body model (HBM) was validated for far side evaluation by means of PMHS tests carried out under six simplified far-side impact conditions. A CORrelation Analysis (CORA) rating was carried out. Based on the CORA score and the proposed biofidelity evaluation procedure the model was considered valid to be used in evaluation of far-side impact countermeasures. The HBM was thereafter positioned in a sled model developed based on the proposed Euro-NCAP 2020 protocol. The predicted risk of rib fractures and lateral head excursion was evaluated both with and without far-side airbag. The proposed far-side airbag was found to reduce head excursion and rib fracture risk in far-side impacts from 900 to 150 impact angles. To assess Euro-NCAP far-side sled test rating performance, a 50%-ile WorldSID crash dummy model was positioned in the sled model. Without countermeasure, the head displacement exceeded the occupant interaction limit. With far-side airbag the head excursion limit was not exceeded. The far-side airbag also reduced chest deflection from above the high-performance limit to below, such that a full score was obtained also for the chest evaluation

Short-term Outcomes in Patients with Carcinoma of the Esophagus and Gastroesophageal Junction Receiving Neoadjuvant Chemotherapy or Chemoradiation before Surgery. A Prospective Study

Background Neoadjuvant chemotherapy (NACT) and neoadjuvant chemoradiotherapy (NACRT) have been demonstrated to improve survival compared to surgery alone in esophageal carcinoma, but the evidence is scarce on which of these therapies is more beneficial, particularly with regard to resectability rates, postoperative morbidity and mortality, and histological responses. Objective This study compares the resectability, pathological response rates, and short-term surgical outcomes in patients with carcinoma of the esophagus or gastroesophageal junction receiving NACT or NACRT prior to surgery. Methods Patients with resectable carcinoma of the esophagus or gastroesophageal junction adenocarcinoma, squamous cell carcinoma, and adenosquamous histologies were enrolled in this well-matched prospective non-randomized study. Thirty-five patients were given NACT, and 35 NACRT. In the NACT group, 25 patients received three cycles of three-weekly carboplatin and paclitaxel, and 10 received three cycles of cisplatin/5-fluorouracil, while all the patients in the NACRT group received 41.4 Gy of radiotherapy concomitant with five cycles of weekly paclitaxel and carboplatin-based chemotherapy. Results Twenty-two patients in the NACT group and 33 patients in NACRT group had resection (P value = 0.0027). The percentage of microscopically margin-negative resection (R0 resection) was similar in both the groups (86% versus 88%). The incidences of surgical and non-surgical complications were similar in both the groups (P=0.34). There was no 30-day mortality. There was a trend toward more pathological complete regression in the NACRT group (P=0.067). The percentage of patients achieving complete tumor regression at the primary site (pT0) was significantly higher in the NACRT group. The down-staging effect on nodal status was similar in both the groups (P=0.55). There was a statistically significant reduction in tumor size in the NACRT group. The median numbers of nodes harvested and positive nodes were similar in both the groups. Conclusion Patients receiving NACRT had better resectability rates and pathological response rates, but similar postoperative morbidity compared to the NACT group

Long-Term Effects of Gene Therapy in a Novel Mouse Model of Human MFRP-Associated Retinopathy

Patients harboring homozygous c.498_499insC mutations in MFRP demonstrate hyperopia, microphthalmia, retinitis pigmentosa, retinal pigment epithelial atrophy, variable degrees of foveal edema, and optic disc drusen. The disease phenotype is variable, however, with some patients maintaining good central vision and cone function till late in the disease. A knock-in mouse model with the c.498_499insC mutation in Mfrp (Mfrp KI/KI) was developed to understand the effects of these mutations in the retina. The model shares many of the features of human clinical disease, including reduced axial length, hyperopia, retinal degeneration, retinal pigment epithelial atrophy, and decreased electrophysiological responses. In addition, the eyes of these mice had a significantly greater refractive error (p < 0.01) when compared to age-matched wild-type control animals. Administration of recombinant adeno-associated virus-mediated Mfrp gene therapy significantly prevented thinning from retinal neurodegeneration (p < 0.005) and preserved retinal electrophysiology (p < 0.001) when treated eyes were compared to contralateral sham-treated control eyes. The Mfrp KI/KI mice will serve as a useful tool to model human disease and point to a potential gene therapeutic approach for patients with preserved vision and electrophysiological responses in MFRP-related retinopathy

A missense mutation in ASRGL1 is involved in causing autosomal recessive retinal degeneration.

Inherited retinal dystrophies are a group of genetically heterogeneous conditions with broad phenotypic heterogeneity. We analyzed a large five-generation pedigree with early-onset recessive retinal degeneration to identify the causative mutation. Linkage analysis and homozygosity mapping combined with exome sequencing were carried out to map the disease locus and identify the p.G178R mutation in the asparaginase like-1 gene (ASRGL1), segregating with the retinal dystrophy phenotype in the study pedigree. ASRGL1 encodes an enzyme that catalyzes the hydrolysis of L-asparagine and isoaspartyl-peptides. Studies on the ASRGL1 expressed in Escherichia coli and transiently transfected mammalian cells indicated that the p.G178R mutation impairs the autocatalytic processing of this enzyme resulting in the loss of functional ASRGL1 and leaving the inactive precursor protein as a destabilized and aggregation-prone protein. A zebrafish model overexpressing the mutant hASRGL1 developed retinal abnormalities and loss of cone photoreceptors. Our studies suggest that the p.G178R mutation in ASRGL1 leads to photoreceptor degeneration resulting in progressive vision loss