Flexible Use Research Articles

Theoretical and experimental analysis of a hybrid industrial robot used for friction stir welding

This paper highlights the main aspects involved in the process of friction stir welding (FSW) realised by means of a robotic manufacturing workstation, showing the outcomes of theoretical and experimental analyses. The cell is equipped with a hybrid industrial robot, whose static performance is successfully exploited for the realisation of welding products with high mechanical properties. The robot flexibility of use is addressed. Several tests allow to gain a deeper understanding of the effect of technological parameters on FSW processes. Such information can be used for the development of model-based controllers, which are assumed to effectively improve accuracy and process stability also in the welding of complex geometries.

Relationship of Lane Width to Capacity for Urban Expressways

To increase the capacity of urban expressways in Shanghai, China, additional lanes were created during the past decade through reconstruction. Field measurements indicate that maximum lane width is 3.97 m and minimum width is only 2.73 m. To investigate the relationship between lane width and capacity for urban expressways, 3 months of traffic flow data were extracted and filtered from the system to manage inductive detectors on Shanghai's urban expressways. Analysis of all 440 segments of expressways in Shanghai showed that only 60 sites could reach their capacity; the characteristics of these 60 sites were further analyzed statistically. An analysis of a variance, a regression analysis, and a t-test were used to explore the relationship between lane width and capacity. The research showed that lane width had no statistically significant effect on capacity. Two causes that might account for this finding are discussed further: (a) free-flow speeds are similar for different lane widths according to the findings of a t-test that found no statistically significant differences and (b) the critical speed when capacity is reached for a Shanghai expressway is very low, only 45 km/h. Thus, drivers can deal with a narrow lane width at such a low critical speed. This finding suggests that geometric design policies for capacity purposes should provide substantial flexibility for use of narrower lane widths on urban expressways with low speed limits, although those lane widths must be subject to safety considerations.

지역아동센터 실내공간의 물리적 환경 특성 사례연구 - 광주광역시 사례를 중심으로 -

Community child center is the facility of the highest number of children in child welfare facilities. But plan for the physical environment is not considered importantly because of insufficient finance. However impact of the physical environment in growing children is very closely related in terms of the emotional as well as a functional perspective. Therefore, it is necessary to understand current physical environment and to seek to find alternative methods that can be resolved space matters. As a basic study for this, in the present study we compare and integrate the design principles of child care facility guidelines. And we set up a framework of analysis to derive the design principles that are required in the target area. It is possible to analyze the environmental characteristics of community child center located in Gwang-ju from this framework, to obtain the flowing results. First, draw items are formation of inner direction, provide of environmental supportability, flexibility of use, healthy space. It can be understood that the emotional aspects and physical aspects should be considered comprehensively. Second, as a result of the case analysis, planning elements consideration of the functional aspects appeared high fulfillment rate generally. Planning elements of low fill rate ascertain result from the process take advantage of the narrow space and it was possible to ascertain the study for flexible utilization of space is not. As a result, in order to improve the problems of the target space, increasing the functionality is necessary and also requires consideration of sensitivity of the user's face.

Factors affecting nebulised medicine adherence in adult patients with cystic fibrosis: a qualitative study

Nebulised medicines contribute to the high treatment burden experienced by patients with cystic fibrosis (CF). This study explored experiences of adult patients with CF when using nebulised medicines, factors impacting on their adherence to nebulised therapy and strategies they used to facilitate adherence. Community setting, in Sydney, Australia. Ten patients with CF were recruited through a CF patient organisation. Semi-structured face-to-face interviews were conducted, addressing the study objectives. Interviews were audio-recorded, transcribed verbatim and content analysed for anticipated and emergent themes. Experiences with using nebulised medicines; and barriers and facilitators of adherence to nebulised medicines. Participants' age ranged from 22 to 45 years, with half being male. Four broad themes (with more specific sub-themes) were identified from the interviews: experiences with using nebulised medicines (cleaning nebuliser, time taken to use nebuliser medicine, flexibility in use of nebuliser); feelings about using nebulised medicines (necessary/important, dislike, part of life); factors impacting non-adherence (time consuming therapy, side effects/effects of medicine, work/social demands, lack of perceived importance); factors and strategies facilitating adherence (perceived medicine importance, habit/routine, support, health benefits, technology/medicine dose form, timetabling). Nebulised therapy for cystic fibrosis patients takes a substantial amount of time, with patients trying to alter their routine to incorporate nebulising into their daily lives. However there are still many factors that lead to low adherence, including work/social demands and travelling. Patients balance the necessity for nebulised therapy against the barriers, and engage in intentional non-adherence at times. Future strategies and resources should target and address specific factors identified by patients with CF as being important and impacting their adherence to nebulised medicines.

An evaluation of the functionality and accessibility of e-readers for individuals with print disabilities

Purpose– This study aims to examine the usability of three popular electronic reading devices (e-readers) to determine which device provides the best functionality for individuals with print disabilities. Adaptability and flexibility for use with assistive technology are also evaluated.Design/methodology/approach– This study reports the results of a usability test of e-readers and their potential for use by individuals with print disabilities. Students enrolled in a School of Library and Information Science evaluated and compared the devices through a series of tasks designed to measure functionality. Participants completed a series of questionnaires and engaged in small group discussion about the efficacy of the devices. Likert scales and open-ended evaluation were employed in the evaluation and analysis.Findings– Two of the three devices examined offered no accessibility features for individuals with low or no vision who require assistive technologies to use information and communication technologies. The third device, while offering greater universal access functionality for individuals with mild-to-moderate print disabilities, also had weaknesses for individuals with severe print disabilities.Originality/value– With the rapid deployment of e-readers, little research has been completed measuring the accessibility and functionality for individuals with print disabilities in library or educational environments. The paper provides data on the usability of e-readers for users with print disabilities and recommendations for adopting e-reader use in libraries and educational environments. It will inform and guide information professionals seeking to provide greater access to resources for patrons with specialized access needs.

Intracranial self-stimulation to evaluate abuse potential of drugs.

Intracranial self-stimulation (ICSS) is a behavioral procedure in which operant responding is maintained by pulses of electrical brain stimulation. In research to study abuse-related drug effects, ICSS relies on electrode placements that target the medial forebrain bundle at the level of the lateral hypothalamus, and experimental sessions manipulate frequency or amplitude of stimulation to engender a wide range of baseline response rates or response probabilities. Under these conditions, drug-induced increases in low rates/probabilities of responding maintained by low frequencies/amplitudes of stimulation are interpreted as an abuse-related effect. Conversely, drug-induced decreases in high rates/probabilities of responding maintained by high frequencies/amplitudes of stimulation can be interpreted as an abuse-limiting effect. Overall abuse potential can be inferred from the relative expression of abuse-related and abuse-limiting effects. The sensitivity and selectivity of ICSS to detect abuse potential of many classes of abused drugs is similar to the sensitivity and selectivity of drug self-administration procedures. Moreover, similar to progressive-ratio drug self-administration procedures, ICSS data can be used to rank the relative abuse potential of different drugs. Strengths of ICSS in comparison with drug self-administration include 1) potential for simultaneous evaluation of both abuse-related and abuse-limiting effects, 2) flexibility for use with various routes of drug administration or drug vehicles, 3) utility for studies in drug-naive subjects as well as in subjects with controlled levels of prior drug exposure, and 4) utility for studies of drug time course. Taken together, these considerations suggest that ICSS can make significant contributions to the practice of abuse potential testing.

Sustainable value stream mapping (Sus-VSM) in different manufacturing system configurations: application case studies

Abstract Achieving sustainability in manufacturing requires a holistic view spanning product design, manufacturing processes, manufacturing systems, and the entire supply chain. Such an approach must be taken to ensure the economic, environmental and societal goals of sustainability are achieved. Value stream mapping (VSM) is an important technique used in Lean manufacturing to identify and visualize waste. However, conventional VSM does not directly consider the environmental or societal performance of production lines. Sustainable VSM (Sus-VSM) is a proposed extension of conventional VSM that incorporates metrics for sustainability. The ability to visually assess manufacturing sustainability through VSM increases its usefulness as a tool to identify potential areas of improvement. This paper will examine in detail three case studies to demonstrate the breadth of applicability of the Sus-VSM tool. The findings from the case studies will be used to further examine the aptness and limitations of the tool in assessing and visualizing sustainability performance in different manufacturing system configurations. Potential avenues to overcome the noted issues are discussed for each case. The presented discussions act to validate the proposed methodology, highlighting its flexibility for use in many manufacturing contexts.

Combustion of propane with Pt and Rh catalysts in a meso-scale heat recirculating combustor

The results obtained from the combustion behavior of propane over platinum and rhodium catalysts in a meso-scale heat recirculating combustor are presented. The extinction limits, conversion, product selectivity/yield, and activation energy using the two catalysts were compared in an effort to predict their performance using a liquid fuel. The extinction limits were also compared to those of non-catalytic combustion in the same combustor. The results showed that the use of a catalyst greatly expanded the range of stable operating conditions, in terms of both extinction limits and flow rates supported. The Rh catalyst was found to exhibit a higher propane conversion rate, reaching a maximum of 90.4% at stoichiometric conditions (as compared to only 61.4% offered by the Pt catalyst under lean conditions), but the Pt catalyst had superior CO2 selectivity for most of the examined conditions, indicating more of the heat released being used for product formation as opposed to being lost to the environment. However, despite having a higher rate of heat loss, the combustion with the Rh catalyst produced an overall higher amount of enthalpy than the Pt due to its superior fuel conversion. The Pt catalyst also had a significantly smaller activation energy (13.8kJ/mol) than the Rh catalyst (74.7kJ/mol), except at equivalence ratios richer than Φ=1.75 (corresponding to catalyst temperatures below 500°C), where it abruptly changed to 211.4kJ/mol, signifying a transition from diffusion-limited reactions to kinetically limited reactions at this point. The results reveal that Rh would be a more suitable catalyst for use in liquid-fueled meso-scale combustors, as fuel conversion has been found to be a limiting factor for combustion stability in these systems, and as its higher output energy allows for greater flexibility of use.

Wave propagation in unsaturated porous media

We present a simple macroscopical three-phase model describing wave propagation in partially saturated porous media. The model consists of a continuous non-wetting phase and a continuous wetting phase and is an extension of classical biphasic (Biot-type) models. The framework is based on kinematics, balance equations and well-known constitutive equations for single- and multi-phase continua. The final set of linearised equations gives information about the physical behaviour of three compressional waves and one shear wave. Among others, information about phase velocities, damping and displacements of the single constituents can be determined for arbitrary variations of input parameters like saturation or angular frequency (ω). The physical processes are investigated and explained by an example of Massilon sandstone filled with air and water. For the quasi-static limit case, i.e. $${\omega \mapsto 0}$$ , the results of the model are identical with the phase velocity obtained with the well-known Gassmann–Wood limit. The model focuses on systems with a liquid and a gas phase. It is shown that the grain compressibility can be neglected in this case, and the amount of material parameters as well as the complexity reduces significantly compared to other three-phase approaches. This makes the well-adapted model suitable for direct application in the vadose zone or partially saturated laboratory samples with a gas phase and a liquid phase. The final model is characterised by low computational effort, general validity for application from geophysics over engineering up to biomedicine and flexibility for use of extended empirical and theoretical relationships.

Inshore Floating LNG for Liquefaction of Onshore Shale Gas

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper OTC 24091, ’Development Options for North American LNG Export: The Merits of Inshore-Deployed FLNG for Liquefaction of Onshore Shale Gas and Examination of Principal Technology Drivers,’ by Joe Verghese, WorleyParsons Europe, and Nancy Ballout, WorleyParsons Houston, prepared for the 2013 Offshore Technology Conference, Houston, 6-9 May. The paper has not been peer reviewed. Copyright 2013 Offshore Technology Conference. Reproduced by permission. The advent of shale-gas production onshore North America, the resulting overhang of gas supplies, and the downward pressure on gas prices have led operators to consider the possibilities of liquid-natural-gas (LNG) liquefaction plants for the export of LNG from coastal locations to international markets. Several proposals for onshore liquefaction relate to the conversion of existing LNG regasification sites. The paper assesses the technology implications of migrating LNG floating production, storage, and offloading (FPSO) concepts to inshore service. Market Context The energy markets have seen a remarkable evolution in gas developments driven by a number of factors including the relative abundance of this energy resource and its global availability, flexibility in use, and low carbon number. According to the International Energy Agency (IEA), gas will increase its share of the global energy mix from 21% in 2009 to 25% by 2035. Against this backdrop, the shale-gas revolution in North America has already led to gas self-sufficiency, with North America poised to be a net exporter by 2016. According to the IEA, the introduction of horizontal drilling, hydrofracturing, and resource targeting technologies has led to a 27% increase in natural-gas production, from 2005 levels to 23 Tcf in 2011 (Fig. 1). A further increase of 44% from this 2011 level is foreseen by 2040. US natural-gas production has outpaced growth in demand by a ratio of 2:1 since 2005, leading to downward pressure on natural-gas prices. These factors have prompted owners of existing LNG regasification terminals to sense a shift in the demand/supply balance, and to seek approval to install liquefaction facilities for export of LNG. By the end of May 2012, 15 applications had been submitted to the US Department of Energy for export authorization, amounting to a staggering 145 million t/a of capacity. The sweet spot for floating liquefaction units lies precisely in the greenfield phase of the LNG-export scenario. For greenfield developments, the atshore or inshore deployment of floating LNG (FLNG) can offer interesting advantages over its onshore counterpart. These include potential for faster permitting, a faster construction schedule, and significant potentials for standardization and redeployment.

Comparison of Geant4 and MCNP6 for use in delayed fission radiation simulation

Neutron induced fission fragment distributions and delayed fission radiation are extremely important with reactor applications in fission cross sections and heating. Data on the fragment distributions are sparse so simulations use models or interpolations between known neutron energies. Different simulations perform different treatments of the distributions, and have different capabilities and flexibility in use. MCNP is a typical workhorse for fission simulations and coupled with burn-up codes such as CINDER can provide delayed radiation from fission. Geant4 is an extremely flexible physics based Monte Carlo simulation framework, but is not typically used for fission research. In this work the applicability of Geant4 for delayed fission radiation simulations is examined, with comparison to MCNP6 coupled with the CINDER2008 burn-up code. The Fisher and Engle fission experiment with the Godiva II subcritical assembly as a fission neutron source is used as a test case. Both simulations are adapted from that experiment and simulation results are compared with that experiment. Following Fisher and Engle, photons/fission/sec, MeV/fission/sec, and MeV/photon are examined. For the first two quantities results from both simulation codes are similar and are lower than experimental values, with Geant4 giving a higher value for earlier time bins and MCNP6/CINDER giving a higher value for the later time bins. For the last quantity both simulations are usually within uncertainty of the experimental values, with MCNP6/CINDER values consistently higher than both experimental and Geant4 values.

Designing, Constructing, and Using Plasma Control System Algorithms on DIII-D

The DIII-D plasma control system (PCS), initially deployed in the early 1990s, now controls nearly all aspects of the tokamak and plasma environment. Versions of this PCS, supported by General Atomics, are presently used to control several tokamaks around the world, including the superconducting tokamaks Experimental Advanced Superconducting Tokamak and Korean Superconducting Tokamak Advanced Research. The experimental challenges posed by the advanced tokamak mission of DIII-D and the variety of devices supported by the PCS have driven the development of a rich array of control algorithms, along with a powerful set of tools for algorithm design and testing. Broadly speaking, the PCS mission is to utilize all available sensors, measurements, and actuators to safely produce a plasma state trajectory leading to and then maintaining the desired experimental conditions. Often new physics understanding leads to new or modified control requirements that use existing actuators in new ways. We describe several important DIII-D PCS design and test tools that support implementation and optimization of algorithms. We describe selected algorithms and the ways they fit within the PCS architecture, which in turn allows great flexibility in designing, constructing, and using the algorithms to reliably produce a desired complex experimental environment. Control algorithms, PCS interfaces, and design and testing tools are described from the perspective of the physics operator (PO), who must operate the PCS to achieve experimental goals and maximize physics productivity of the tokamak. For example, from a POs (and experimental team leader's) standpoint, a PCS algorithm interface that offers maximum actuator, algorithmic, and measurement configuration flexibility is most likely to produce a successful experimental outcome. However, proper constraints that limit flexibility in use of the PCS can also help to maximize effectiveness. For example, device limits and safety must be built into the PCS, sometimes at the algorithm level. We show how the DIII-D PCS toolset enables rapid offline testing of a new or modified algorithm in a simulated tokamak environment. Finally, we illustrate usage of PCS-based checklists and procedures that enhance experimental productivity, and we describe an asynchronous condition detector system within the PCS that enhances device safety and enables complex experiment design.

Fast, Versatile, and Low-Cost Interface Circuit for Electrochemical and Resistive Gas Sensor

Chemical sensors for gas detection nowadays are widely used in several applications; basically, electrochemical sensors and semiconductor devices are used for this purpose. In both cases, the sensor value estimation is usually implemented as a current measurement and they are often referred as current-output sensors. In this paper, a versatile and low-cost interface circuit for such kind of sensors is presented. The proposed solution is characterized by a wide measurement range, yielding flexibility of use with sensors showing different baseline values. In addition, the fast readout time, on the order of tens of milliseconds, guarantees an accurate acquisition of the sensor data even in presence of fast transients, for example when using sensors operated in pulsed thermal regimes. The front-end works with a single-voltage power supply and furnishes a time-coded digital output signal, thus it is suitable to be directly interfaced to a microcontroller for the management of the measurement process, data elaboration, and presentation. Simplicity and compactness of the electronic interface make possible the integration in a single-chip solution, together with the digital electronics. Reproducibility of the circuit, for applications requiring the simultaneous acquisition of multiple sensors, is furthermore facilitated. The proposed approach has been validated with experimental tests conducted on a discrete component prototype. The system characterization has shown a maximum linearity error in the estimation of the sensor current or resistance of ~ 5% over a measurement range of seven decades; the measurement time is in all the considered input range. Fast thermal transients of different semiconductor sensors for gas sensing have been successfully acquired, demonstrating the validity of the proposed approach. Power dissipation ( at 3.3 V) and the front-end cost ( ~ 10 $) make the presented solution suitable for the employment in low-cost and low-power gas detection systems.

Not so bird-brained: Pigeons show what-where-when memory both as time of day and how long ago.

In an ever-changing world, the ability to track what significant events occur and where and when is beneficial to a variety of animal species. The purpose of the present studies was to assess the presence of this ability to track what-where-when memory in pigeons based both on when during the day the events occurred and how long ago events occurred. In these studies, pigeons were trained to discriminate between two foods that differed in quality (what), making one more "attractive" than the other. The birds were required to alter their choice of keylights (where) to get these differential foods based on the time of day (Experiments 1-2) or how long ago (Experiments 3-5) they were in a session (when). Pigeons were able to correctly choose the key that yielded the "attractive" food using both time of day and how long ago, indicating a what-where-when memory. However, the pigeons failed to transfer this knowledge to a novel situation, showing limited flexibility in use of the learned what-where-when information. These findings suggest that pigeons have abilities to track what-where-when events as do caching birds and other animal species, but perhaps represented in a more rigid manner.

Usefulness of two bioeconomic frameworks for evaluation of community-initiated species conservation projects

Context Community-based conservation managers and their funding providers must apportion limited resources to potential projects that provide varying biodiversity benefits. Funding applicants must demonstrate that proposed projects are likely to provide positive conservation returns on investments. Aims We investigated the practical usefulness of two bioeconomic frameworks, the Project Prioritisation Protocol and the Investment Framework for Environmental Resources (INFFER) in guiding community-based conservation funding decisions and the benefits and challenges to community groups in evaluating projects using the tools. Methods We evaluated four species-based community-led conservation projects in New Zealand using the tools, and assessed the quality, relevance and potential impact of the frameworks to community conservation, including users’ perceptions of their usefulness. Key results Benefit–cost metrics from both tools indicated that all four projects would provide a low return on investment. However, both tools were highly sensitive to key assumptions about the values of conservation assets (species) being managed and the values of predicted differences made by projects. Both tools scored well against criteria used to assess their technical ‘quality’. INFFER had greater flexibility for use in different situations, but its use by community groups may be constrained by the time demands of completing a full project evaluation. Both tools can help users define problems and formulate innovative solutions through assessment of success and risk factors and the identification of project efficiencies. Conclusions Although both tools provide quantitative, transparent processes for the relative evaluation and ranking of competing projects, their sensitivities to species and/or asset valuation and benefit estimates mean that users should not accept scores and project rankings uncritically. For community groups, evaluation frameworks are likely to be useful to document costs, conservation benefits and risk factors accurately and transparently, and can encourage applicants to develop more robust approaches to project management, including the development of specific and measurable management objectives. Implications Adoption of more transparent and standardised assessment of funding applications by agencies, despite some of the drawbacks of currently available tools, would facilitate more transparent prioritisation of competing funding bids and would encourage community groups to develop a more robust approach to project design and management.

Development of Re-Setting Toxin Delivery Devices and Long-Life Lures for Rats

Author(s): Murphy, Elaine; Sjoberg, Tim; Barun, Arijana; Aylett, Paul; MacMorran, Duncan; Eason, Charles | Abstract: Introduced rats continue to have a major impact on biodiversity around the world, and improved control techniques are required to avoid further extinctions. We are trialing re-setting toxin-delivery systems (Spitfires) targeting a range of predators, including rats. The rat Spitfire works by firing 800 mg of a toxic paste onto the belly of the rat as it passes through a tunnel; the device then resets. When the rats groom the paste from their fur, they ingest the toxin. Each Spitfire is capable of approximately 100 doses and is fitted with a counter and a delay mechanism. We trialed 0.55% 1080 paste in the Spitfire and 15 of 15 wild Norway rats and 14 of 15 black rats died. Further trials are planned with a range of toxins to allow flexibility of use. Resetting devices that are expected to work for long periods without being serviced also require long-life lures. Preliminary trials showed urine and scats from female Norway rats were attractive to both male and female Norway rats. The volatile components from these and further trials will be identified to aid in developing a long-life lure. The long-term, effective control of introduced rats will require a range of toxins with different modes of action, a number of different delivery systems, and long-life lures.

A Multi-disciplinary Modeling Technique for Requirements Management in Mechatronic Systems Engineering

Abstract Machines and plants continuously increase in complexity due to higher customer expectations regarding their purpose and flexibility of use. For this reason, machines and plants development processes need to adapt continuously to the present situation. In addition, the growing meaning of electronic and software components in machines and plants complicates the engineering since the interaction of different disciplines leads to increasing coordination efforts and problems regarding the interface between these disciplines. To face these challenges, the suitable handling of arising requirements is one key factor for the success of engineering processes. Therefore, a multi-disciplinary modeling technique for requirements management is presented in this paper. After a summary of approaches for model-based development and requirements management in the context of mechatronic systems engineering, the modeling technique with its concepts, terms, tasks and workflows is illustrated. To demonstrate the feasibility of the proposed approach, the modeling technique was applied to a miniaturized packaging plant, which is currently developed at the Institute for Machine Tools and Industrial Management (iwb) of Technische Universitat Munchen for teaching students and benchmarking engineering methods and tools. Finally, an outlook with extensions of the concept for fault-tolerant systems and the integration of further engineering tools in order to promote a consistent engineering tool-chain is given.

Cyclic chlorine trap-doping for transparent, conductive, thermally stable and damage-free graphene.

We propose a novel doping method of graphene using the cyclic trap-doping method with low energy chlorine adsorption. Low energy chlorine adsorption for graphene chlorination avoided defect (D-band) formation during the doping by maintaining the π-bonding of the graphene, which affects conductivity. In addition, by trapping chlorine dopants between the graphene layers, the sheet resistance could be decreased by ∼ 88% under optimized conditions. Among the reported doping methods, including chemical, plasma, and photochemical methods, the proposed doping method is believed to be the most promising for producing graphene with extremely high transmittance, low sheet resistance, high thermal stability, and high flexibility for use in various flexible electronic devices. The results of Raman spectroscopy and sheet resistance showed that this method is also non-destructive and controllable. The sheet resistance of the doped tri-layer graphene was 70 Ω per sq. at transmittance of 94%, and which was maintained for more than 100 h in a vacuum at 230 °C. Moreover, the defect intensity of graphene was not increased during the cyclic trap-doping.

LTE Cellular Network Planning for Urban Area

Due to the advancement of telecommunication platform, users are now demanding new applications such as Online Gaming, mobile TV, Web 2.0, and to meet this requirement operators needed to design more flexible network. To fulfill the requirements, 3rd Generation Partnership Project (3GPP) works on the Long Term Evolution (LTE) and propose a system which has larger bandwidths (up to 20 MHz), low latency and packet optimized radio access technology having peak data rates of 100 Mbps in downlink and 50 Mbps in the uplink (Magdalena, 2007; Motorola, 2007; Skold, 2009). Offering a greater coverage by providing higher data rates over wider areas and flexibility of use at existing and new frequency bands plan is a major challenge. In this paper, we are analyzing practical coverage scenario in an urban area (i.e. Kolkata) in terms of received signal levels, total noise, interference, throughput, and quality factor for downlink signal level.

Adjusting biomaterial composition to achieve controlled multiple-day release of dexamethasone from an extended-wear silicone hydrogel contact lens

Purpose: To alter the composition and structure of silicone hydrogel contact lenses to achieve controlled release of dexamethasone and evaluate the lens optical and mechanical properties compared to commercial lenses. There is a tremendous need for controlled release of drugs from ocular biomaterials as the majority of ophthalmic drugs are delivered via topical eye drops, which have low bioavailability and patient compliance.Methods: Poly(PDMS-co-TRIS-co-DMA) contact lenses were synthesized with varying PDMS/TRIS:DMA ratios (0.25:1, 0.67:1, 1.5:1) as well as with additional crosslinking monomers. Lenses were characterized via in vitro release studies in a microfluidic device at ocular flowrates and in large well-mixed volumes, optical quality studies over visible wavelengths, mechanical analysis, and determination of polymer volume fraction in the swollen state.Results: Extended and controlled release of therapeutically relevant concentrations of dexamethasone was achieved for multiple day, continuous wear up to 60 days at in vitro ocular flowrates. Release was delayed due to a combination of increased hydrophobic to hydrophilic composition and the inclusion of additional structural constraints, both of which decreased the polymer volume fraction in the swollen state. However, decreased mass release rates were at the expense of increased modulus and decreased lens flexibility. All lenses had high optical clarity (∼90% transmittance) and contained highly oxygen permeable siloxane composition similar to those found in commercial silicone hydrogel lenses, but they had poor flexibility for use as soft contact lenses.Conclusions: Based on our results, the lenses described herein likely have too high of a modulus for use as extended-wear, soft contact lenses with drug release. Therefore, other controlled release methods would be better suited for maintaining adequate mechanical properties and achieving controlled and extended release for the duration of wear in soft, silicone hydrogel contact lens biomaterials. However, these biomaterials may find clinical use as more rigid gas permeable contact lenses or inserts.