Dynamic Service Rate Control for a Single Server Queue with Markov Modulated Arrivals

We consider the problem of service rate control of a single server queueing system with a finite-state Markov-modulated Poisson arrival process. We show that the optimal service rate is non-decreasing in the number of customers in the system; higher congestion rates warrant higher service rates. On the contrary, however, we show that the optimal service rate is not necessarily monotone in the current arrival rate. If the modulating process satisfies a stochastic monotonicity property the monotonicity is recovered. We examine several heuristics and show where heuristics are reasonable substitutes for the optimal control. None of the heuristics perform well in all the regimes. Secondly, we discuss when the Markov-modulated Poisson process with service rate control can act as a heuristic itself to approximate the control of a system with a periodic non-homogeneous Poisson arrival process. Not only is the current model of interest in the control of Internet or mobile networks with bursty traffic, but it is also useful in providing a tractable alternative for the control of service centers with non-stationary arrival rates.Comment: 32 Pages, 7 Figure

Tubular Electrospun Composite Scaffolds for Potential Bone Tissue Engineering

poster abstractElectrospinning is an adaptable method in which polymer solutions or melts converted into micro or nano scale fibers. In this procedure, polymer solutions are loaded into 10 mL syringes that contained millimeter scale nozzles. High voltage (20-30 kV) was applied to polymer solutions at the tip of the nozzle to stabilize the surface tension by electrostatic force. The critical point where this stabilization occurred is called Taylor cone and it lets the droplets to turn into polymer sprays. The fibers were collected onto a tubular rotational collector, which was grounded. Different tubular scaffolds composed of pure polycaprolactone (PCL), small intestinal submucosa (SIS), hydroxyapatite (HA) and tricalciumphosphate (TCP) were prepared by using the electrospinning technique. 13 and 15 wt% pure PCL stock solutions were prepared by dissolution in 1,1,1,3,3,3-hexafluoro-2-propanol (HPF) and stirring at the room temperature until a viscous translucent liquid was acquired. Composite PCL/SIS and PCL/HA dopes were prepared from 10 wt% PCL stock by adding SIS or HA in an 8:1 (PCL:SIS, PCL:HA) dry weight ratio. Similarly, PCL/HA/TCP solutions were made from 13 wt% PCL stock by adding HA and TCP in a 8:1:1 dry weight ratio. Each individual scaffold will be scanned through electron microscope (ECM) to gather information about the % porosity and the diameter of the electrospun fibers. Mechanical testing will be conducted to measure the tensile strength of the fibers. Finally, implanting the tubular scaffolds into axolotls will test cell biocompatibility of the scaffolds

Electrical Characteristics of Polypropylene Mixed with Natural Nanoclay

Polypropylene has been used in radio-frequency capacitors and has also started to be employed in cables as insulation. The objective of this study was to evaluate the electrical properties of polypropylene filled with natural clay as a nano-material. Polypropylene samples having 0%, 2% and 6% natural clay by weight were exposed to 60-Hz sinusoidal voltages at two different rates of rise. The breakdown voltage of each sample was recorded at these different ramp rates. Also, the Root-mean-squared (rms) current was measured as the voltage was increased across the test samples. The important findings of this study were (a) the breakdown strength of the natural nanoclay-filled polypropylene was higher than the unfilled polypropylene, and the optimum concentration of nanoclay appeared to be 2% by weight; (b) the current density as a function of the electric-field intensity indicated a non-linear behavior with saturation, and the saturation onset took place at a higher electric-field intensity in nanoclay-filled polypropylene, wherein 2% nanoclay seemed to be the optimum concentration as well for the onset electric field of saturation

Designing touch screen user interfaces for future flight deck operations

Many interactional issues with Flight Management Systems (FMS) in modern flight decks have been reported. Avionics designers are seeking for ways to reduce cognitive load of pilots with the aim to reduce the potential for human error. Academic research showed that touch screen interfaces reduce cognitive effort and provide an intuitive way of interaction. A new way of interaction to manipulate radio frequencies of avionics systems is presented in this paper. A usability experiment simulating departures and approaches to airports was used to evaluate the interface and compare it with the current system (FMS). In addition, interviews with pilots were conducted to find out their personal impressions and to reveal problem areas of the interface. Analyses of task completion time and error rates showed that the touch interface is significantly faster and less prone to user input errors than the conventional input method (via physical or virtual keypad). Potential problem areas were identified and an improved interface is suggested

Target size guidelines for interactive displays on the flight deck

The avionics industry is seeking to understand the challenges and benefits of touchscreens on flight decks. This paper presents an investigation of interactive displays on the flight deck focusing on the impact of target size, placement and vibration on performance. A study was undertaken with search and rescue (SAR) crew members in an operational setting in helicopters. Results are essential to understand how to design effective touchscreen interfaces for the flight deck. Results show that device placement, vibration and target size have significant effects on targeting accuracy. However, increasing target size eliminates the negative effects of placement and vibration in most cases. The findings suggest that 15 mm targets are sufficiently large for non-safety critical Electronic Flight Bag (EFB) applications. For interaction with fixed displays where pilots have to extend their arms, and for safety critical tasks it is recommended to use interactive elements of about 20 mm size

Target size guidelines for interactive displays on the flight deck

The avionics industry is seeking to understand the challenges and benefits of touchscreens on flight decks. This paper presents an investigation of interactive displays on the flight deck focusing on the impact of target size, placement and vibration on performance. A study was undertaken with search and rescue (SAR) crew members in an operational setting in helicopters. Results are essential to understand how to design effective touchscreen interfaces for the flight deck. Results show that device placement, vibration and target size have significant effects on targeting accuracy. However, increasing target size eliminates the negative effects of placement and vibration in most cases. The findings suggest that 15 mm targets are sufficiently large for non-safety critical Electronic Flight Bag (EFB) applications. For interaction with fixed displays where pilots have to extend their arms, and for safety critical tasks it is recommended to use interactive elements of about 20 mm size

Industry sponsorship bias in research findings: a network meta-analysis of LDL cholesterol reduction in randomised trials of statins

Objective: To explore the risk of industry sponsorship bias in a systematically identified set of placebo controlled and active comparator trials of statins. Design: Systematic review and network meta-analysis. Eligibility Open label and double blind randomised controlled trials comparing one statin with another at any dose or with control (placebo, diet, or usual care) for adults with, or at risk of developing, cardiovascular disease. Only trials that lasted longer than four weeks with more than 50 participants per trial arm were included. Two investigators assessed study eligibility. Data sources Bibliographic databases and reference lists of relevant articles published between 1 January 1985 and 10 March 2013. Data extraction One investigator extracted data and another confirmed accuracy. Main outcome measure Mean absolute change from baseline concentration of low density lipoprotein (LDL) cholesterol. Data synthesis Study level outcomes from randomised trials were combined using random effects network meta-analyses. Results: We included 183 randomised controlled trials of statins, 103 of which were two-armed or multi-armed active comparator trials. When all of the existing randomised evidence was synthesised in network meta-analyses, there were clear differences in the LDL cholesterol lowering effects of individual statins at different doses. In general, higher doses resulted in higher reductions in baseline LDL cholesterol levels. Of a total of 146 industry sponsored trials, 64 were placebo controlled (43.8%). The corresponding number for the non-industry sponsored trials was 16 (43.2%). Of the 35 unique comparisons available in 37 non-industry sponsored trials, 31 were also available in industry sponsored trials. There were no systematic differences in magnitude between the LDL cholesterol lowering effects of individual statins observed in industry sponsored versus non-industry sponsored trials. In industry sponsored trials, the mean change from baseline LDL cholesterol level was on average 1.77 mg/dL (95% credible interval −11.12 to 7.66) lower than the change observed in non-industry sponsored trials. There was no detectable inconsistency in the evidence network. Conclusions: Our analysis shows that the findings obtained from industry sponsored statin trials seem similar in magnitude as those in non-industry sources. There are actual differences in the effectiveness of individual statins at various doses that explain previously observed discrepancies between industry and non-industry sponsored trials

Mixed method approach in designing flight decks with touch screens: a framework

Touch screen technology’s first public appearance was in the early 2000s. Touch screens became a part of the daily life with the invention of smartphones and tablets. Now, this technology has the potential to be the next big change in flight deck design. To date, mobile devices are deployed by several air carriers to perform a host of non-safety critical pre-flight and in-flight tasks. Due to high safety requirements requested by authorities, new technologies cannot be adopted as fast as in other settings. Flight deck evolution, which is briefly presented in this paper, is reflecting this natural time delay. Avionics manufacturers are exploring and working on future concepts with touch screen displays. This paper investigates the potential benefits and challenges of touch screen technology on flight decks by means of a variety of qualitative and quantitative research methods (mixed method approach). On the basis of this, a framework was constructed showing the relation between various aspects that could impact the usability of touch screens on the flight deck. This paper concludes with a preliminary questionnaire that can help avionic designers to evaluate whether a touch screen is an appropriate user interface for their system

Future flight decks: impact of +Gz on touchscreen usability

Future flight deck designs from various avionics manufacturer incorporate touchscreen technology. There is little published research investigating the impact of inflight vibrations and increased G-Force (+Gz) on touchscreen usability. A Fitts’ law experiment was conducted to understand the effect of +Gz on touchscreen usability. 2-Gz and 3-Gz conditions were simulated with a weight-adjustable wristband. Empirical results and subjective ratings showed a large impact of +Gz on performance and fatigue indices. While the simulated +Gz increased linearly, throughput decreased exponentially, and movement time increased exponentially. This was also reflected by subjective ratings across all conditions. Findings suggest to transfer the experimental setting into a more realistic environment (human centrifuge) where ecological validity can be achieved

Have Usability and Security Trade-offs in Mobile Financial Services (MFS) become Untrustworthy?

The trade-off between Usability and Security has been well researched with various models proposed on how best to improve Usability without jeopardizing Security and vice visa. Usable Security has become a key factor in Mobile Financial Services (MFS), the new frontier for mobile phones utilisation. However, have the compromises gone too far? The trustworthiness of MFS system has already slowed down new adoption and impacted ongoing security trust issues and user confidence in spite of potential MFS benefits for its users. To understand this growing lack of trust with MFS, we need to comprehend the nature of Usable Security in assuring the behaviours of MFS users and determine the right trade-off to improve trust whilst facilitating future uptake. We conducted an empirical survey of 698 user’s experience of MFS and here present our findings of this investigation for further synthesis towards proposing practical control elements to assure Usable Security in MFS