bluuebunny/crossref_metadata_2025 huggingface dataset:
Model Comparisons of Competing Risk and Recurrent Events for Graft Failure in Renal Transplant Recipients
Authors: Holme Ingar , Fellström Bengt C. , Jardine Alan G. , Hartmann Anders , Holdaas Hallvard
Published: November 2012

Background and objectives

Risk factor analysis of long-term graft survival in kidney transplant recipients is usually based on Cox regression models of time to first occurrence of doubling of serum creatinine or graft loss (DSCGL). However, death is a competing cause of failure, and censoring patients who die could bias estimates. We therefore compared estimates of time to first event versus estimates that included death as a competing risk and recurrent events.

Design, setting, participants, & measurements

A Cox regression analysis of 1997–2002 data from the Assessment of Lescol in Renal Transplant (ALERT) trial population identified an eight-factor risk model, by analyzing time to first occurrence of DSCGL. The same factors were re-analyzed, allowing for death as competing. The probability of survival free of DSCGL was estimated; and two recurrent models (marginal and conditional) were used for time to events.

Results

Creatinine, systolic BP, and HLA-DR mismatches lost 33%–46% of their strength of association with DSCGL when death was included as a competing risk. Small changes were observed if recurrent events were analyzed in the marginal model.

Conclusion

The relationship between serum creatinine and DSCGL was attenuated when death was considered as a competing risk; inclusion of recurrent events had little effect. These findings have important implications for analysis and trial design in populations at high mortality risk.
Biodiesel from rapeseed variety "Banacanka" using KOH catalyst
Authors: Micic Radoslav , Tomic Milan , Simikic Mirko , Zarubica Aleksandra
Published: November 2012

This paper presents a complete characterization of rapeseed oil, of Banacanka
variety, as well as the potential use of oil generated after filtering, in
order to obtain biodiesel. Researches are based on the fact that Banacanka is
the oldest domestic rapeseed variety, the so-called double zero "00" (low in
erucic acid, below 5%, and glucosinolates below than 30 mmol g-1), suitable
for use in the region, since it is low temperatures tolerant, posseses high
genetic potential for seed yield of about 5.2 t/ha, and high oil content of
around 45%. Transesterification was carried out in batch reactor Parr 4520,
with KOH as a catalyst. Cold pressed oil without prior treatment was used as
feedstock for transesterificataion. The paper analyses the effects of
temperature, reaction duration, catalyst amount and rate of agitation on the
synthesis of biodiesel at constant pressure and molar methanol/oil
ratio.
Transitioning to IFRS in Australian Classrooms: Impact on Teaching Approaches
Authors: Jackling Beverley , de Lange Paul A. , Natoli Riccardo
Published: November 2012

This paper outlines the impact that transition to International Financial Reporting Standards (IFRS) had in Australia with reference to the teaching approaches across university accounting classrooms. The discussion begins with a short history of past rules governing accounting in Australia, followed by a review of the transition to IFRS in Australia. An assessment of the ways in which the Australian accounting academic community incorporated the adoption of IFRS into their curriculum is also provided. The review suggests that despite an initial period of foreboding from accounting educators, the transition to IFRS involved minimal changes in teaching approaches. We argue that there were missed opportunities to revise the curriculum, particularly at the introductory level, by adopting a framework-based teaching approach in line with the principles-based IFRS. The paper concludes with some observations about lessons learned from the Australian experience as a guide for accounting faculty in other parts of the world who are about to embark on the transition to IFRS.
On a question of A. Schinzel: Omega estimates for a special type of arithmetic functions
Authors: Kühleitner Manfred , Nowak Werner
Published: November 2012

The paper deals with lower bounds for the remainder term in asymptotics for a certain class of arithmetic functions. Typically, these are generated by a Dirichlet series of the form ζ 2(s)ζ(2s−1)ζ M(2s)H(s), where M is an arbitrary integer and H(s) has an Euler product which converges absolutely for R s > σ0, with some fixed σ0 < 1/2.
Paraneoplastic pemphigus associated with dendritic cell neoplasm and Castleman’s disease: report of a new case and review of the literature
Authors: Roca Bernardino , Pitarch Gerard , Soler Francisco , Penades Maria , Resino Elena , Roca Manuel
Published: November 2012

We report on a patient with longstanding multicentric Castleman’s disease, hyaline-vascular type, who developed a follicular dendritic cell sarcoma, and finally presented a fatal paraneoplastic pemphigus. We review all four cases of such a triple association described in the literature so far.
Automatic diagnosis of primary headaches by machine learning methods
Authors: Krawczyk Bartosz , Simić Dragan , Simić Svetlana , Woźniak Michał
Published: November 2012

Primary headaches are common disease of the modern society and it has high negative impact on the productivity and the life quality of the affected person. Unfortunately, the precise diagnosis of the headache type is hard and usually imprecise, thus methods of headache diagnosis are still the focus of intense research. The paper introduces the problem of the primary headache diagnosis and presents its current taxonomy. The considered problem is simplified into the three class classification task which is solved using advanced machine learning techniques. Experiments, carried out on the large dataset collected by authors, confirmed that computer decision support systems can achieve high recognition accuracy and therefore be a useful tool in an everyday physician practice. This is the starting point for the future research on automation of the primary headache diagnosis.
An efficient method for the preparation of benzyl γ-ketohexanoates
Authors: Iqbal Muhammad , Baloch Imam , Baloch Musa
Published: November 2012

Twenty acid chlorides, 4-(mono/di-benzyloxy)-4-ketobutanoyl chlorides (Ia–XXa) were synthesised by the reaction of monoesters of succinic acid with thionyl chloride. The product thus obtained (4-benzyloxy-4-ketobutanoyl chlorides) was treated with diethylcadmium to convert it into the corresponding keto-esters (Ib–XXb), the mono/di-benzyl-γ-ketohexanoates, with a good yield. All the compounds thus prepared were characterised by physical, spectroscopic (UV-VIS, IR, 1H NMR, 13C NMR), and mass measurements techniques.
Single-Step Test for Unilateral Limb Ability Following Total Knee Arthroplasty
Authors: Marmon Adam Rubin , McClelland Jodie A. , Stevens-Lapsley Jennifer , Snyder-Mackler Lynn
Published: November 2012

Study Design

Secondary analysis of a cohort enrolled in a prospective, randomized, longitudinal clinical trial.

Objectives

The single-step test (SST) was evaluated to assess its intertester reliability, validity as a test of activity limitation, and responsiveness to change for patients after unilateral total knee arthroplasty (TKA). The SST was also examined to determine whether it could differentiate between the surgical and nonsurgical lower limbs of patients after unilateral TKA and between the surgical limbs of patients after TKA and the limbs of healthy controls.

Background

Tests of functional ability for patients recovering from TKA cannot differentiate the contribution of each limb to performance outcome. A test of unilateral limb ability would provide a metric for assessing the surgical lower extremity, without the confounder of the status of the contralateral lower extremity.

Methods

Intertester reliability was assessed between clinicians and between a clinician and a switch mat. Patients who underwent unilateral TKA were tested at initial outpatient physical therapy evaluation, at 3 months after TKA, and at 1 year after TKA.

Results

The assessment of function with the SST was determined to be reliable between testers when using a stopwatch. SST times were significantly correlated with other measures of lower extremity functional performance, providing evidence of its validity in patients after TKA. The SST was responsive to treatment in patients after TKA, with improvements in time for test completion. Performance on the SST also differed between limbs of patients after TKA and when comparing the limbs of healthy controls to those of patients after TKA.

Conclusion

The SST is a reliable measure between testers and a valid and responsive test of activity limitations when assessing unilateral lower extremity impairments in patients after TKA. J Orthop Sports Phys Ther 2013;43(2):66–73. Epub 16 November 2012. doi:10.2519/jospt.2013.4372
Clinimetric Analysis of Pressure Biofeedback and Transversus Abdominis Function in Individuals With Stabilization Classification Low Back Pain
Authors: Grooms Dustin R. , Grindstaff Terry L. , Croy Theodore , Hart Joseph M. , Saliba Susan A.
Published: November 2012

Study Design

Descriptive laboratory study.

Objective

To determine if a proposed clinical test (pressure biofeedback) could detect changes in transversus abdominis (TrA) muscle thickness during an abdominal drawing-in maneuver.

Background

Pressure biofeedback may be used to assess abdominal muscle function and TrA activation during an abdominal drawing-in maneuver but has not been validated.

Methods

Forty-nine individuals (18 men, 31 women) with low back pain who met stabilization classification criteria underwent ultrasound imaging to quantify changes in TrA muscle thickness while a pressure transducer was used to measure pelvic and spine position during an abdominal drawing-in maneuver. A paired t test was used to compare differences in TrA activation ratios between groups (able or unable to maintain pressure of 40 ± 5 mmHg). The groups were further dichotomized based on TrA activation ratio (high, greater than 1.5; low, less than 1.5). Sensitivity, specificity, and likelihood ratios were calculated.

Results

There was not a significant difference (P = .57) in TrA activation ratios (able to maintain pressure, 1.59 ± 0.28; unable to maintain pressure, 1.54 ± 0.24) between groups. The pressure biofeedback test had low sensitivity of 0.22 (95% confidence interval [CI]: 0.10, 0.42) but moderate specificity of 0.77 (95% CI: 0.58, 0.89), a positive likelihood ratio of 0.94 (95% CI: 0.33, 2.68), and a negative likelihood ratio of 1.02 (95% CI: 0.75, 1.38).

Conclusion

Successful completion on pressure biofeedback does not indicate high TrA activation. Unsuccessful completion on pressure biofeedback may be more indicative of low TrA activation, but the correlation and likelihood coefficients indicate that the pressure test is likely of minimal value to detect TrA activation. This study was registered with ClinicalTrials.gov (NCT01015846). J Orthop Sports Phys Ther 2013;43(3):184–193. Epub 16 November 2012. doi:10.2519/jospt.2013.4397
Issues Affecting the Delivery of Physical Therapy Services for Individuals With Critical Illness
Authors: Pawlik Amy J. , Kress John P.
Published: November 2012

Research supports the provision of physical therapy intervention and early mobilization in the management of patients with critical illness. However, the translation of care from that of well-controlled research protocols to routine practice can be challenging and warrants further study. Discussions in the critical care and physical therapy communities, as well as in the published literature, are investigating factors related to early mobilization such as transforming culture in the intensive care unit (ICU), encouraging interprofessional collaboration, coordinating sedation interruption with mobility sessions, and determining the rehabilitation modalities that will most significantly improve patient outcomes. Some variables, however, need to be investigated and addressed specifically by the physical therapy profession. They include assessing and increasing physical therapist competence managing patients with critical illness in both professional (entry-level) education programs and clinical settings, determining and providing an adequate number of physical therapists for a given ICU, evaluating methods of prioritization of patients in the acute care setting, and adding to the body of research to support specific functional outcome measures to be used with patients in the ICU. Additionally, because persistent weakness and functional limitations can exist long after the critical illness itself has resolved, there is a need for increased awareness and involvement of physical therapists in all settings of practice, including outpatient clinics. The purpose of this article is to explore the issues that the physical therapy profession needs to address as the rehabilitation management of the patient with critical illness evolves.
The Six-Minute Walk Test in Chronic Pediatric Conditions: A Systematic Review of Measurement Properties
Authors: Bartels Bart , de Groot Janke F. , Terwee Caroline B.
Published: November 2012

Background

The Six-Minute Walk Test (6MWT) is increasingly being used as a functional outcome measure for chronic pediatric conditions. Knowledge about its measurement properties is needed to determine whether it is an appropriate test to use.

Purpose

The purpose of this study was to systematically review all published clinimetric studies on the 6MWT in chronic pediatric conditions.

Data Sources

The databases MEDLINE, EMBASE, CINAHL, PEDro, and SPORTDiscus were searched up to February 2012.

Study Selection

Studies designed to evaluate measurement properties of the 6MWT in a chronic pediatric condition were included in the systematic review.

Data Extraction

The methodological quality of the included studies and the measurement properties of the 6MWT were examined.

Data Synthesis

A best evidence synthesis was performed on 15 studies, including 9 different chronic pediatric conditions. Limited evidence to strong evidence was found for reliability in various chronic conditions. Strong evidence was found for positive criterion validity of the 6MWT with peak oxygen uptake in some populations, but negative criterion validity was found in other populations. Construct validity remained unclear in most patient groups because of methodological flaws. Little evidence was available for responsiveness and measurement error. Studies showed large variability in test procedures despite existing guidelines for the performance of the 6MWT.

Limitations

Unavailability of a specific checklist to evaluate the methodological quality of clinimetric studies on performance measures was a limitation of the study.

Conclusions

Evidence for measurement properties of the 6MWT varies largely among chronic pediatric conditions. Further research is needed in all patient groups to explore the ability of the 6MWT to measure significant and clinically important changes. Until then, changes measured with the 6MWT should be interpreted with caution. Future studies or consensus regarding modified test procedures in the pediatric population is recommended.
Effects of a Data-Driven District Reform Model on State Assessment Outcomes
Authors: Slavin Robert E. , Cheung Alan , Holmes GwenCarol , Madden Nancy A. , Chamberlain Anne
Published: November 2012

A district-level reform model created by the Center for Data-Driven Reform in Education (CDDRE) provided consultation with district leaders on strategic use of data and selection of proven programs. Fifty-nine districts in seven states were randomly assigned to CDDRE or control conditions. A total of 397 elementary and 225 middle schools were followed over a period of up to 4 years. In a district-level hierarchical linear modeling (HLM) analysis controlling for pretests, few important differences on state tests were found 1 and 2 years after CDDRE services began. Positive effects were found on reading outcomes in elementary schools by Year 4. An exploratory analysis found that reading effects were larger for schools that selected reading programs with good evidence of effectiveness than for those that did not.
Assessment of Advanced Dispatching Measures for Recovering Disrupted Railway Traffic Situations
Authors: Corman Francesco , D'Ariano Andrea
Published: November 2012

Railway timetables are developed to make operations robust and resilient to small delays. However, disturbances perturb the daily plan, and dispatchers need to adjust the plan to keep operations feasible and to limit delay propagation. For large infrastructure disruptions, the available railway capacity is reduced, and the timetable could become infeasible. The paper studies how to support dispatchers in the management of traffic flow during disruptions. A set of disruption resolution scenarios to manage seriously disturbed traffic conditions in large networks is investigated. For instance, in the case of track blockage, train services can be canceled, rerouted in the disrupted dispatching area, or rerouted in other areas while still with the same origin and destination. Feasible and efficient operations schedules are found quickly by an advanced decision support system for dispatching known as ROMA (railway traffic optimization by means of alternative graphs), which is based on microscopic detail and can handle large areas by decomposition. Detailed performance indicators can be computed to let dispatchers choose a specific solution, for example, by minimizing train delays and reducing passengers' discomfort. In the computational experiments, an analysis is done of a blockage on a double track line, combined with multiple entrance delays on a large railway network with heavy traffic. Several disruption resolution scenarios involving cancellation of services, rerouting, and shuttle trains are considered, and each feasible plan is evaluated in relation to travel times, frequency of services, and delay propagation.
Decision Support System to Optimize Railway Stopping Patterns
Authors: Jong Jyh-Cherng , Suen Chian-Shan (James) , Chang S. K. (Jason)
Published: November 2012

An intercity passenger rail is built to connect several major cities. To provide satisfactory services to passengers, railway operators plan different stop schedules, such as all-stop, skip-stop, and express services. However, stopping patterns determined by empirical rules or political arguments are generally not optimal. This paper aims at developing a decision support system to generate the optimal combination of stopping patterns for minimizing total passenger in-vehicle time. This problem was first formulated by using mixed integer programming, but this method is intractable when dealing with large-scale problems because of the complexity of model structure and the nature of the problem. A genetic algorithm was then developed to search for the optimal or near-optimal solution efficiently within a reasonable computation time. The proposed algorithm was successfully implemented on Taiwan High Speed Rail. The resulting solution is better than the current practice, and the proposed algorithm is capable of finding the optimal solution in seconds. The present case study demonstrates that the decision support tool can tackle large-scale problems and can help operators efficiently and effectively design an optimal combination of stopping patterns.
Risk Assessment of Positive Train Control by Using Simulation of Rare Events
Authors: Meyers Timothy , Stambouli Amine , McClure Karen , Brod Daniel
Published: November 2012

The risk assessment of positive train control (PTC) presents a number of challenges that can be addressed through simulation, a common tool for analyzing large, complex stochastic systems. The combined analysis of a simulated rail system with safety models that track the propagation of human errors and equipment failures toward hazards and accidents (or their eventual safe resolution) enables the prediction of accidents and their probability of occurrence for a base case without PTC and an alternate case with PTC. Accidents are rare events, and when probabilities of rare events are estimated, efficiency is a major concern because the computer resources required for statistically reliable estimates are usually overwhelming. The problem of efficiency can be addressed through multilevel splitting, or staged simulation. The basic idea of splitting is to create separate copies of the simulation whenever it approaches the rare event. The FRA generalized train movement simulator (GTMS) integrates a rail system simulator with safety models and staged simulation to arrive at metrics of safety and risk that meet federal regulatory requirements. The simulation techniques used and a description of their implementation in the GTMS are presented. The paper concludes with a case study risk assessment that uses the GTMS of a nonvital overlay PTC system for a Class I railroad.
Development of the Next Generation of Intercity Corridor Bi-Level Equipment with Crash Energy Management
Authors: Martinez Eloy , Nelson Frances , Prabhakaran Anand , Jones Antony
Published: November 2012

An innovative rail car procurement specification was developed for bi-level equipment. This specification was developed to fulfill the Passenger Rail Investment and Improvement Act of 2008 (PRIIA). PRIIA is a congressional mandate to the National Railroad Passenger Corporation, state departments of transportation, FRA, and passenger rail car builders and suppliers to develop the next generation of passenger rail equipment for intercity corridor service for speeds up to 125 mph. Technological innovations are to be used to improve safety incrementally, and components are to be standardized to the extent possible to leverage economies of scale to help revitalize the manufacturing base for domestic passenger equipment. This paper focuses on the technical discussions held by a cross section of key industry stakeholders to develop specification language for crash energy management features as an overlay on a fully compliant bi-level car design. The purpose of the paper is to widely disseminate the methodology and process used and to provide background information on the values chosen for individual car crush zone performance.
Slab Track Mass-Spring System
Authors: Tomicic-Torlakovic Mirjana , Budisa Miodrag , Radjen Vidan
Published: November 2012

Development of a ballastless slab track structure with a mass-spring system began about 20 years ago, and different kinds of these track systems have been successfully in use for urban transportation systems. With these systems the elastic elements are inserted under the slabs to provide protection from bothersome vibration and noise. The paper explains the principal aspects of calculation verifications by means of a simulation model for the selected type of mass-spring track system.
Comparison of Magnitude of Actions on Track in High-Speed and Heavy-Haul Railroads
Authors: Giannakos Konstantinos
Published: November 2012

In modern high-speed railways the necessity for achieving low life-cycle costs has led to a well-compacted—almost undeflected—substructure. Applications of excellent quality substructure are encountered in the French network with the operation of high-speed trains (TGV in French) and also in research projects of the International Union of Railways. The countervailing need for increased elasticity in the track's structure is satisfied by the development of the highly resilient fastenings with soft pads. There is a long-standing discussion about whether these soft pads promote a sufficient life cycle for heavy-haul railways as well, as in the case of the U.S. railways. In this paper a parametric investigation using a theoretical approach is performed to estimate the actions on track support points (ties) in high-speed and heavy-haul lines with four methods found in the international literature; parameter values, mainly coefficients of stiffness, derived from measurements on the track are used. Because the life cycle of the pads and the clips of the fastenings are dependent on the actions exerted on each tie per passing axle and the number of axle passes, this investigation leads to significant ascertainments for comparing the actions on the track in both cases.
Movement of Water through Ballast and Subballast for Dual-Line Railway Track
Authors: Ghataora Gurmel S. , Rushton Ken
Published: November 2012

The purpose of effective track design is to ensure that load from trains can be safely supported by subgrade soils, which are likely to be affected by water. Because it is almost impossible to prevent water from entering the ballasted track and therefore affecting the underlying layers, it is vitally important that water can drain away rapidly. The study undertaken shows how water moves through a dual-railway track, which is either symmetrical about the centerline or superelevated with a continuous slope of the subgrade across both tracks. The study shows that water may be retained in the track nearest the drain for more than a week with possible consequential impact on increased deformation and therefore the need for more maintenance. It also shows that a high permeability composite may be included near the base of the subballast to effect significant improvement in track drainage.
Stochastic Rail Wear Model for Railroad Tracks
Authors: Costello Seosamh B. , Premathilaka Anuradha S. , Dunn Roger C. M.
Published: November 2012

This paper describes the development of a stochastic rail wear model. Once validated, the model can be used to assist in the strategic assessment of railroad track funding needs. The algorithms used for simulating rail wear use Markov processes, and the resulting transition probability matrix defines rail wear progression, as opposed to the more familiar regression-type model popular with engineers. The New Zealand railroad track database contained 10 years of rail wear data from which to develop and validate the model. The transition probability matrices for use in the model were developed with the first 5 years of the historical rail wear data, with the remaining 5 years set aside to validate the model. The development of the transition probability matrices is reported in the paper, together with the development of the initial condition distributions ready for use in validation of the model.
Development of Base Train Equivalents to Standardize Trains for Capacity Analysis
Authors: Lai Yung-Cheng (Rex) , Liu Yun-Hsuan , Lin Tzu-Ya
Published: November 2012

A conventional railway system usually has multiple train types with various service patterns operating on the same line. Differences in train characteristics lead to varied capacity effects on the system. “Rail line capacity” is commonly defined as the maximum number of trains that can be operated on a section of track with an expected level of service within a given time period. However, a particular unit (trains/hour or trains/ day) does not reflect the train type the unit refers to. In this study, a new concept is proposed, namely, the base train equivalent (BTE), along with a standardization process to classify different train types in accordance with the particular type defined by the user. This concept is similar to the passenger car equivalent, which converts trucks to passenger car units in classifying highway transportation. A delay-based approach is also developed to determine BTEs on the basis of results obtained from two common capacity evaluation methods: parametric capacity analysis and simulation. With the proposed method, capacity measurements from different lines or systems can be compared and evaluated, resulting in meaningful and useful attributes.
Analysis of Causes of Major Train Derailment and Their Effect on Accident Rates
Authors: Liu Xiang , Saat M. Rapik , Barkan Christopher P. L.
Published: November 2012

Analysis of the causes of train accidents is critical for rational allocation of resources to reduce accident occurrence in the most cost-effective manner possible. Train derailment data from the FRA rail equipment accident database for the interval 2001 to 2010 were analyzed for each track type, with accounting for frequency of occurrence by cause and number of cars derailed. Statistical analyses were conducted to examine the effects of accident cause, type of track, and derailment speed. The analysis showed that broken rails or welds were the leading derailment cause on main, yard, and siding tracks. By contrast to accident causes on main tracks, bearing failures and broken wheels were not among the top accident causes on yard or siding tracks. Instead, human factor–related causes such as improper use of switches and violation of switching rules were more prevalent. In all speed ranges, broken rails or welds were the leading cause of derailments; however, the relative frequency of the next most common accident types differed substantially for lower-versus higher-speed derailments. In general, at derailment speeds below 10 mph, certain track and human factor causes—such as improper train handling, braking operations, and improper use of switches—dominated. At derailment speeds above 25 mph, those causes were nearly absent and were replaced by equipment causes, such as bearing failure, broken wheel, and axle and journal defects. These results represent the first step in a systematic process of quantitative risk analysis of railroad freight train safety, with an ultimate objective of optimizing safety improvement and more cost-effective risk management.
Holistic Approach to Airport Surface Safety
Authors: Wilke Sabine , Majumdar Arnab , Ochieng Washington Y.
Published: November 2012

Airport surface safety is acknowledged worldwide as a key area to aviation safety. However, current methods for analyzing and mitigating surface safety occurrences are piecemeal in their approach and limited in scope and perspective. This paper emphasizes the need for a holistic approach to surface safety and introduces a new methodology for the development of a holistic taxonomy for critical factors underlying airport surface safety occurrences. The taxonomy incorporates findings from the relevant literature, safety data, airport surveys, and interviews with subject matter experts. It benefits from the viewpoints of all the relevant aviation stakeholders (regulators, air navigation service providers, airport authorities, airlines, ground handling companies, accident investigation boards) and derives its robustness from the combination of a number of research methods. The application of the taxonomy to support the safety risk management function within the context of safety management systems is proposed. Application of the taxonomy to a multinational data set (North America, Europe, Oceania) verifies that the databases complement each other and that a holistic picture can only be achieved through their combined use. In addition, the analysis indicates that differences in the data sets are a function of the national air traffic system and airport infrastructure, underlying regulations, reporting system and safety culture, and the viewpoint of the aviation stakeholder that is represented. Finally, the holistic approach proposed in this paper is shown to be transferable to other areas of aviation safety.
Intercity Passenger Rail Access to Airports
Authors: Sperry Benjamin R. , Larson Shawn , Leucinger David , Janowiak Scott , Morgan Curtis A.
Published: November 2012

The increased demand for air travel and diminishing airport capacity, coupled with a new role for passenger rail in intercity corridors across the United States, have renewed interest in the development of intermodal connections between airports and intercity passenger rail among transportation planners and policy makers. As a result, there is a need for a better understanding of who might be using such connections and how the connections might support intermodal travel activities. This paper examines the characteristics of passengers using the airport–intercity passenger rail interface at the Milwaukee, Wisconsin, airport—one of only four such direct connections currently in existence in the United States. In addition to providing a sustainable alternative to automobile ground access trips to the airport, intercity passenger rail at the Milwaukee airport has expanded the airport's market area well into the Chicago, Illinois, region, approximately 80 mi to the south. The findings indicate that passengers value the convenience and reliability of the service in choosing intercity passenger rail to access the airport. Airport and intercity passenger rail planners are encouraged to consider the findings of this paper in planning activities for future airport–intercity passenger rail interfaces.
Valuing Aviation Noise with the Contingent Valuation Method
Authors: Chalermpong Saksith , Klaiklueng Apipat
Published: November 2012

Aviation noise from Suvarnabhumi Airport, Bangkok, Thailand, has had a severe impact on the quality of life of people who live in the surrounding areas since the airport began operation in 2006. The airport authority offered to buy homes in the most severely affected areas or to provide funds to soundproof them, but the compensation program was aimed mainly at homeowners, not renters of apartments or dormitories. In previous studies in Thailand, the focus was on examining the noise depreciation of home values by hedonic price modeling. In this paper, the scope of previous research is broadened to include the noise impact on renters by using the contingent valuation method to examine their willingness to accept compensation (WTA) when the noise level increases. Estimation of WTA was based on a choice experiment in which subjects were asked to evaluate alternatives in hypothetical scenarios and to select their preferred alternative. Scenarios with various levels of flight frequency and amounts of compensation were systematically developed to study trade-off behavior between these attributes. Coefficient estimates of the multinomial logit model imply that the WTA for an increase of one flight movement ranges from 18.87 to 68.62 baht (US$0.63 to US$2.29) per month. The results of this study can be useful in informing the airport authority's noise compensation policy, which needs to be revised in the near future in light of plans for the airport's expansion.
Minimization of Potential Air Conflicts through Speed Regulation
Authors: Rey David , Rapine Christophe , Fondacci Rémy , El Faouzi Nour-Eddin
Published: November 2012

This paper addresses the speed regulation problem in air traffic management. Because global air traffic volume is continuously increasing, improvement in air traffic control has become a priority. During this decade, European and United States initiatives have been launched to design the future of air traffic management. One of their objectives is to increase air traffic density and optimize flight route plans. This can be achieved through en route deconfliction. Air conflicts have the potential to occur when two or more aircraft are predicted to be below a separation norm in the near future. Such situations affect air traffic controllers' workload; thus, these situations limit controllers' capacity to deal with large numbers of aircraft and induce flight delay. Reducing air traffic controllers' potential workload through speed regulation has been investigated in the En Route Air Traffic Soft Management Ultimate System project. Efficiency of the method has been validated through simulations, including human-in-the-loop experiments, which opens the door to conflict resolution algorithms based on speed regulation. In this paper a formulation for the speed regulation problem is proposed. First, a potential conflict detection and resolution framework is presented. Uncertainty is then introduced in the model, with the aim of reproducing realistic air navigation conditions. A case study of real air traffic instances is described, and results are discussed to assess the potential of the proposed algorithm.
Effect of Pavement Damping and Aircraft Speed on Stress-Based Load Transfer Efficiency
Authors: Joshi Akshay P. , Mehta Yusuf A. , Cleary Douglas
Published: November 2012

This paper documents a study of the dynamic mechanical responses of rigid pavement at the joint under moving aircraft loads. The MRC (pavement constructed on conventional base) section of Construction Cycle 2 test pavement at FAA's National Airport Pavement Test Facility was modeled with the three-dimensional finite element program ABAQUS. The model was calibrated by determining pavement damping parameters and joint stiffness values on the basis of heavy weight deflectometer data and strain profiles captured from dynamic sensors installed within the pavement at various locations. The effect of moving aircraft under varying speeds on tensile strains at the bottom of the portland cement concrete at the joint (εcritical) and dynamic stress-based load transfer efficiency [LTE (S)] at the joint is studied with three-dimensional finite element analysis. A decrease in εcritical at the joint with increasing speed was observed. The dynamic LTE (S) at the joint was enhanced at higher speeds. Sensitivity of dynamic LTE (S) at the joint to pavement damping was also studied with the finite element model. The dynamic LTE (S) at the joint increased with pavement damping. Finally, the effect of aircraft load and wheel configuration on dynamic LTE (S) was studied. Dynamic LTE (S) was sensitive to aircraft wheel configuration; however, it was insensitive to the magnitude of load.
Developing an Empirical and Risk-Based Revenue Forecasting Model for NAV CANADA
Authors: Cripwell J. Paul
Published: November 2012

Accurate forecasting of aviation activity is necessary for NAV CANADA, because the act that created the company stipulates that revenues must equal cost commitments related to the provision of air navigation services. Accurate forecasting of revenue is an important early step in determining the cost commitments that can be met in upcoming fiscal years. Traditional econometric forecasting techniques are of a long-term nature and do not consider the seasonality of traffic, nor do they provide the required detail at the level of the individual month. For these and other reasons, empirical forecasting methods were developed as the primary forecasting approach for the company. This paper describes the selection and development of the empirical model, which is based on the Holt–Winters multiplicative method, for the air traffic that overflies Canadian airspace on routes between North America and Europe. A second part of the modeling process is the application of risk analysis not only to replace current scenario-based methods but also to improve and augment them. The methodology will then be applied to the two other markets, Asia and the Far East and Alaska, with eventual expansion to Canadian air traffic, though they are not discussed in this paper.
Leveraging Fuel Cost Differences in Aircraft Routing by considering Fuel Ferrying Strategies
Authors: Kheraie Ali Zockaie , Mahmassani Hani S.
Published: November 2012

The focus of this study is on the aircraft routing problem and the potential role of a ferrying strategy for fueling the aircraft. The main contribution is to estimate the cost of maintenance routing when fuel ferrying strategies are considered. A combined model of aircraft routing and fuel management is developed and applied for three scenarios of fuel cost distribution in a small conceptual network with five stations and 18 flight legs. The results show that fuel cost variations make the ferrying strategy effective in the aircraft routing problem.
Accounting for Systematic Influences on Preference Heterogeneity in Air Travel
Authors: Rezaei Ali , Puckett Sean M.
Published: November 2012

Modeling passengers' itinerary choice behavior helps in understanding the increasingly competitive airline market and in predicting air travel demand. Recently, investigation of the variation in passengers' preferences with regard to factors influencing their choice through estimation of the mixed multinomial logit model has received attention. An extended form of the model identifies sources of heterogeneity and consequently makes the choice models less restrictive in considering both systematic and random preference variation across individuals. This research investigates the existence of significant interactions between passengers' preference heterogeneity around the mean of random parameters in estimated utility functions and observed sociodemographic or trip-related attributes in the case of air travel. Unlike previous research in the literature that has focused on choice behavior modeling in mature markets with relatively high per capita rates of air travel activity, this study centers on a survey of travelers in Tehran, Iran, a low-propensity air travel market. Several distributions for random parameters are considered to test the impacts of restricting distributions to allow only normality. The potential to improve model fit with alternative distributions was confirmed. The findings suggest that differences in the marginal utilities can be explained mostly by differences in travel experience. More experienced passengers are less sensitive to fare and more sensitive to flight level-of-service attributes. Furthermore, the estimated distributions of willingness-to-pay (WTP) measures confirm the value of accounting for interactions between preference heterogeneity and observed variables and in this case yield higher mean WTP values than does analysis that omits these interaction effects.
Importance of a Resilient Air Services Network to Australian Remote, Rural, and Regional Communities
Authors: Donehue Paul , Baker Douglas , Washington Simon
Published: November 2012

Rural, regional, and remote settlements in Australia require resilient infrastructure to remain sustainable in a context characterized by frequent large-scale natural disasters, long distances between urban centers, and the pressures of economic change. A critical aspect of this infrastructure is the air services network, a system of airports, aircraft operators, and related industries that enables the high-speed movement of people, goods, and services to remote locations. A process of deregulation during the 1970s and 1980s resulted in many of these airports passing into local government and private ownership, and the rationalization of the industry saw the closure of a number of airlines and airports. This paper examines the impacts of deregulation on the resilience of air services and the contribution that they make to regional and rural communities. In particular, the robustness, redundancy, resourcefulness, and rapidity of the system are examined. The conclusion is that while the air services network has remained resilient in a situation of considerable change, the pressures of commercialization and the tendency to manage aspects of the system in isolation have contributed to a potential decrease in overall resilience.
Comparing indocyanine green videoangiography to the gold standard of intraoperative digital subtraction angiography used in aneurysm surgery
Authors: Washington Chad W. , Zipfel Gregory J. , Chicoine Michael R. , Derdeyn Colin P. , Rich Keith M. , Moran Christopher J. , Cross DeWitte T. , Dacey Ralph G.
Published: November 2012

Object

The purpose of aneurysm surgery is complete aneurysm obliteration while sparing associated arteries. Indocyanine green (ICG) videoangiography is a new technique that allows for real-time evaluation of blood flow in the aneurysm and vessels. The authors performed a retrospective study to compare the accuracy of ICG videoangiography with intraoperative angiography (IA), and determine if ICG videoangiography can be used without follow-up IA.

Methods

From June 2007 through September 2009, 155 patients underwent craniotomies for clipping of aneurysms. Operative summaries, angiograms, and operative and ICG videoangiography videos were reviewed. The number, size, and location of aneurysms, the ICG videoangiography and IA findings, and the need for clip adjustment after ICG videoangiography and IA were recorded. Discordance between ICG videoangiography and IA was defined as ICG videoangiography demonstrating aneurysm obliteration and normal vessel flow, but post-IA showing either an aneurysmal remnant and/or vessel occlusion requiring clip adjustment.

Results

Thirty-two percent of patients (49 of 155) underwent both ICG videoangiography and IA. The post-ICG videoangiography clip adjustment rate was 4.1% (2 of 49). The overall rate of ICG videoangiography–IA agreement was 75.5% (37 of 49) and the ICG videoangiography–IA discordance rate requiring post-IA clip adjustment was 14.3% (7 of 49). Adjustments were due to 3 aneurysmal remnants and 4 vessel occlusions. These adjustments were attributed to obscuration of the residual aneurysm or the affected vessel from the field of view and the presence of dye in the affected vessel via collateral flow. Although not statistically significant, there was a trend for ICG videoangiography–IA discordance requiring clip adjustment to occur in cases involving the anterior communicating artery complex, with an odds ratio of 3.3 for ICG videoangiography–IA discordance in these cases.

Conclusions

These results suggest that care should be taken when considering ICG videoangiography as the sole means for intraoperative evaluation of aneurysm clip application. The authors further conclude that IA should remain the gold standard for evaluation during aneurysm surgery. However, a combination of ICG videoangiography and IA may ultimately prove to be the most effective strategy for maximizing the safety and efficacy of aneurysm surgery.
Pneumonia in patients with severe head injury: incidence, risk factors, and outcomes
Authors: Wang Kuo-Wei , Chen Han-Jung , Lu Kang , Liliang Po-Chou , Huang Chun-Kai , Tang Pi-Lien , Tsai Yu-Duan , Wang Hao-Kuang , Liang Cheng-Loong
Published: November 2012

Object

The reported incidence of hospital-acquired bacterial pneumonia in critically ill trauma patients varies from as low as 4% to as high as 87%, with fatality rates varying from 6% to 59%. Clinical studies have identified the risk factors for pneumonia. The authors undertook this retrospective study to evaluate the incidence, risk factors, and outcomes of hospital-acquired bacterial pneumonia in a group of patients with severe head injuries.

Methods

This was a retrospective review of consecutive adult patients admitted to the neurosurgical ICU in the authors' hospital because of severe head injury (Glasgow Coma Scale scores ≤ 8) between January 2008 and December 2010.

Results

During the study period, 290 patients were admitted to the neurosurgical ICU. Multivariate Cox regression analysis showed that age (HR 1.01, 95% CI 1.001–1.02), nasogastric tube insertion (HR 4.56, 95% CI 1.11–18.64), and hemiplegia or hemiparesis (HR 3.79, 95% CI 2.01–7.17) were significantly associated with the development of pneumonia.

Conclusions

The authors identified 3 risk factors (age, nasogastric tube insertion, and hemiplegia or hemiparesis) associated with the development of pneumonia in patients with severe head injury. This finding constituted the basis for developing a simple screening tool that can be used to assess the risk of occurrence of pneumonia in such patients.