Quantification of the inherent uncertainty in the relaxation modulus and creep compliance of asphalt mixes

Advanced material characterization of asphalt concrete is essential for realistic and accurate performance prediction of flexible pavements. However, such characterization requires rigorous testing regimes that involve mechanical testing of a large number of laboratory samples at various conditions and set-ups. Advanced measurement instrumentation in addition to meticulous and accurate data analysis and analytical representation are also of high importance. Such steps as well as the heterogeneous nature of asphalt concrete (AC) constitute major factors of inherent variability. Thus, it is imperative to model and quantify the variability of the needed asphalt material’s properties, mainly the linear viscoelastic response functions such as: relaxation modulus, \(E(t)\), and creep compliance, \(D(t)\). The objective of this paper is to characterize the inherent uncertainty of both \(E(t)\) and \(D(t)\) over the time domain of their master curves. This is achieved through a probabilistic framework using Monte Carlo simulations and First Order approximations, utilizing \(E^{*}\) data for six AC mixes with at least eight replicates per mix. The study shows that the inherent variability, presented by the coefficient of variation (COV), in \(E(t)\) and \(D(t)\) is low at small reduced times, and increases with the increase in reduced time. At small reduced times, the COV in \(E(t)\) and \(D(t)\) are similar in magnitude; however, differences become significant at large reduced times. Additionally, the probability distributions and COVs of \(E(t)\) and \(D(t)\) are mix dependent. Finally, a case study is considered in which the inherent uncertainty in \(D(t)\) is forward propagated to assess the effect of variability on the predicted number of cycles to fatigue failure of an asphalt mix.     

Effect of the genetic background on the reproduction of leptin-deficient obese mice

Obesity is often associated with an impairment of the hypothalamic-pituitary-gonadal axis. The leptin-deficient ob/ob mouse model is characterized by a morbid obesity with a sterility in males and females that is corrected by continuous leptin treatment. Since ob/ob mice are maintained on the C57BL/6J inbred genetic background, we sought to determine whether their infertility can be corrected without leptin treatment but via the effect of modifier genes brought into the obese-sterile phenotype by a different genetic background. Thus, we generated via an F2 intercross ob/ob mice on a mixed C57BL/6J-BALB/cJ genetic background and assayed them for fertility by mating with wild-type C57BL/6J mice. Whereas genetically heterogeneous F2 obese females remained sterile like male and female C57BL/6J ob/ob mice, 41% of F2 C57BL/6J-BALB/cJ obese males were capable of reproducing despite a morbidly obese state. Therefore, the sterility of the original C57BL/6J ob/ob mouse model was genetically corrected independently of its obese state via the effects of modifier genes. Unlike testosterone levels, triglyceride levels, and testes weight-to-body weight ratios, which were all higher in fertile vs. sterile mice, glucose levels were similar in both groups, indicating that the underlying hyperglycemia of ob/ob mice was not an impediment to the onset of fertility. A genome-wide scan in F2 ob/ob males resulted in the localization of four modifier loci on chromosomes 1, 3, 5, and 14 with respective quantitative traits consisting of number of pregnancies, testes weights normalized to body weights, body weight at 8 weeks of age, and circulating testosterone. We conclude that the inheritance of modifier genes at the identified loci acts to promote fertility of otherwise sterile leptin-deficient obese male mice.     

A maximum power point tracker for PV systems using a high performance boost converter

This work deals with the design and experimental implementation of a MPP-tracker for photovoltaic systems, which is a high efficiency dc/dc boost converter operating in continuous conduction mode (CCM). The converter is able to draw maximum power from the PV panel for a given solar radiation level and environment temperature by adjusting the duty cycle of the converter. Additionally, a passive nondissipative turn-on turn-off snubber is used, so that high efficiency and reduced electromagnetic interference (EMI) levels due to the soft switching operation can be obtained. The snubber improves the converter efficiency since the energy that would be dissipated during turning on and turning off is transferred to the load. The control technique, implemented with a single-chip microcontroller 80C51, is based on the perturbation and observation method, where the maximum power point is tracked with periodical calculation of the panel output power. Simulation and experimental results describe the performance of the proposed MPP-tracker.     

Chemical processing of modified lead titanate

A modified lead titanate composition has been synthesized by two different chemical techniques. The influence of the powder processing methods and the calcination temperatures on the physical characteristics, e.g. surface area and phase compositions of the powders, has been investigated. Powders of the same composition have also been prepared by attrition milling the raw materials. Results of the preliminary investigations indicate that the above physical characteristics are strongly dependent on the powder processing methods and calcination temperatures.     

Cold abscess of the chest wall: a surgical entity?

BACKGROUND: Cold abscesses of the chest wall are rare tuberculous locations. Because of the resurgence of tuberculosis, this diagnosis must be considered more frequently. METHODS: During a 15-year period (1980 to 1995), 18 patients with one or more cold abscesses of the chest wall were managed in our department. Epidemiologic characteristics, indications, methods and results of operation, and pathogenesis of the abscesses were considered in this retrospective study. RESULTS: Most of the patients were immigrant men. A previous history of tuberculosis was noted in 15 cases (83%). Six patients had concomitant active pulmonary tuberculosis. There was mostly a solitary lesion in the chest wall, the most frequent location being the rib shaft (60%). Before operation the diagnosis was confirmed only in 4 patients (by needle aspiration of the abscess) and presumed in 4 others: an antituberculous chemotherapy was therefore given preoperatively to 8 patients. One patient did not undergo operation after a favorable response to medical treatment. In the other patients, an operation was indicated because of lack of response in 5 patients and the absence of diagnosis in 12 patients. Adequate debridement and a postoperative antituberculous regimen were performed with recurrence prevention in mind. A follow-up was obtained in 11 of the 17 patients undergoing operation. The only patient who required a second operation because of a recurrence at the same location had refused the antituberculous therapy after the first surgical procedure. Locations of the abscesses, computed tomographic scan results, and histologic examinations are in favor of a lymph-borne dissemination of tubercle bacilli. CONCLUSIONS: Because fine-needle aspiration remains an inaccurate diagnostic tool and antituberculous medical treatment is not always efficient, chest wall tuberculous cold abscesses remain in most cases a surgical entity.     

Agenesis of the internal carotid artery associated with an aneurysm of the anterior communicating artery

We report a case of agenesis of the internal carotid artery which was revealed by a subarachnoid hemorrhage. Angiography showed a ruptured aneurysm of the anterior communicating artery and unilateral absence of the left internal carotid artery. Both the left anterior and middle cerebral arteries were perfused from the right carotid artery via the anterior communicating artery. Absence of the left carotid canal was proved on bone CT. Such an association is discussed. An hemodynamic stress on a congenital defect of the cerebral arterial wall could be the origin of the aneurysm development.     

Effectiveness of the earth tube heat exchanger system coupled to a space model in achieving thermal comfort in rural areas

The aim of this work is to investigate by modelling the possibility of reducing the operational energy of a typical house without negatively affecting its embodied energy. This is done through consideration of different building materials coupled with the use of an earth to air heat exchanger (EAHE) for fresh air supply and cooling. For known indoor and outdoor conditions and for given building materials (thermal capacity and conductance), a ventilation controller determines the amount of flow rate needed to temperate the indoor air temperature to achieve thermal comfort. Different wall configurations are assumed for each of the living zone and the bedroom zone of the apartment. It is found that the use of an optimal wall configuration in each zone coupled with the EAHE results in 76.7% energy savings compared with the reference case with conventional cooling.     

Evaluation of Low-Power Computing when Operating on Subsets of Multicore Processors

Given the accelerated growth in tablet devices, smartphones, and netbooks, designers are faced with serious challenges to meet the needs of mobility in terms of battery life and form factor. It is vital to investigate how to deliver the best mobile experience to users while ensuring adequate levels of performance. In this paper, we present a power management evaluation of multi-core processor systems by comparing thermal power, battery life, and performance when running different types of workloads under a limited number of cores. To show the potential gains from a system power management perspective, we have assessed a mobile platform featuring the Second Generation Intel Core i5 processor, and tested it on a wide selection of workloads and benchmarks. Experimental results show significant thermal power reduction (up to 40 %) in a variety of scenarios, while system performance was sustained in most cases but sacrificed in a few other uncommon situations.