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Search Results: 1 - 10 of 5705 matches for " Sara Cecchetti "
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The Mathematics of the Relationship between the Default Risk and Yield-to-Maturity of Coupon Bonds
Sara Cecchetti,Antonio Di Cesare
Quantitative Finance , 2012,
Abstract: The paper analyzes the mathematics of the relationship between the default risk and yield-to-maturity of a coupon bond. It is shown that the yield-to-maturity is driven not only by the default probability and recovery rate of the bond but also by other contractual characteristics of the bond that are not commonly associated with default risk, such as the maturity and coupon rate of the bond. In particular, for given default probability and recovery rate, both the level and slope of the yield-to-maturity term structure depend on the coupon rate, as the higher the coupon rate the higher the yield-to-maturity term structure. In addition, the yield-to-maturity term structure is upward or downward sloping depending on whether the coupon rate is high or low enough. Similar qualitative results also holds for CDS spreads. Consequently, the yield-to-maturity is an indicator that must be used cautiously as a proxy for default risk.
Ascent Trajectories of Multistage Launch Vehicles: Numerical Optimization with Second-Order Conditions Verification
Mauro Pontani,Giampaolo Cecchetti
ISRN Operations Research , 2013, DOI: 10.1155/2013/498765
Abstract: Multistage launch vehicles are employed to place spacecraft and satellites in their operational orbits. Trajectory optimization of their ascending path is aimed at defining the maximum payload mass at orbit injection, for specified structural, propulsive, and aerodynamic data. This work describes and applies a method for optimizing the ascending path of the upper stage of a specified launch vehicle through satisfaction of the necessary conditions for optimality. The method at hand utilizes a recently introduced heuristic technique, that is, the particle swarm algorithm, to find the optimal ascent trajectory. This methodology is very intuitive and relatively easy to program. The second-order conditions, that is, the Clebsch-Legendre inequality and the conjugate point condition, are proven to hold, and their fulfillment enforces optimality of the solution. Availability of an optimal solution to the second order is an essential premise for the possible development of an efficient neighboring optimal guidance. 1. Introduction Multistage rockets are employed to place spacecraft and satellites in their operational orbits. The optimization of their ascending trajectory leads to determining the maximum payload mass that can be inserted in the desired orbit. This goal is achieved by finding the optimal control time history and the optimal thrust and coast durations. The numerical solution of aerospace trajectory optimization problems has been pursued with different approaches in the past. Indirect methods, such as the gradient-restoration algorithm [1, 2] and the shooting method [3] or direct techniques, such as direct collocation [4, 5], direct transcription [6, 7], and differential inclusion [8, 9], are examples of such techniques. However, only a relatively small number of publications are concerned with trajectory optimization of multistage launch vehicles [1, 2, 10, 11]. A recently published paper [12] describes a simple method for performance evaluation through generation of a near optimal trajectory for a multistage launch vehicle. This research considers the optimal exoatmospheric trajectory of the upper stage of the latter rocket, whose characteristics are specified. The trajectory arc that precedes orbital injection is composed of two phases: (1) coast (Keplerian) arc and (2) thrust phase. More specifically, for the upper stage the existence and duration of a coast arc (with no propulsion) and the optimal thrust direction are being investigated through the first-order necessary conditions for optimality, that is, the Euler-Lagrange equations and the
Prevalência do aleitamento materno na regi?o noroeste de Campinas, S?o Paulo, Brasil, 2001
Cecchetti, Daniel Felipe Alves;Moura, Erly Catarina;
Revista de Nutri??o , 2005, DOI: 10.1590/S1415-52732005000200004
Abstract: objective: to calculate the prevalence of breast-feeding among children less than two years old, in the northwest region of the city of campinas, s?o paulo, brazil. methods: a survey was conducted in 2001, with 4 103 children, querying about birth date, gender, feeding practices and health services routinely used. the questionnaire was applied at the 42 public immunization centers during the 2001 national campaign against polyomielites. the child's diet was categorized as exclusive breast-feeding, predominant breast-feeding, continued breast-feeding and bottle-feeding. results: the prevalences of the exclusive and the total breast-feeding in the first semester were, respectively, 31.6%, and 74.5%. among children aged from six to twelve months, 38.0% were breast-fed. in the second year, the prevalence of breast-feeding was reduced to 22.1%. exclusive breast-feeding changed from 72.2% at the 7th day of life, to 53.8% at the 15th day, to 33.3% at the 3rd month, to 10.0% at the 4th, and to 5.7% at the 6th month. the total breast-feeding prevalence was 100.0% at the 7th day, 79.1% at the 3rd month, 54.3% at the 6th, 34.4% at the 12th, 26.1% at the 18th, and none at the 24th month. exclusive and the total breast-feeding medians were, respectively, 67 days and 6.6 months. among children who attended the public health system, 42.2% were breast-fed, against 34.4% of those who attended a private service (p<0.00001).the protecting effect of the public health service remained, when the statistic model was adjusted for age; conversely, it vanished, when variables like income and maternal education were included in the model. conclusion: the prevalence of breast-feeding is below official recommendations.
Homotopy Perturbation Method for Solving Moving Boundary and Isoperimetric Problems  [PDF]
Sara Ghaderi
Applied Mathematics (AM) , 2012, DOI: 10.4236/am.2012.35062
Abstract: In this paper, homotopy perturbation method is applied to solve moving boundary and isoperimetric problems. This method does not depend upon a small parameter in the equation. homotopy is constructed with an imbedding parameter p, which is considered as a “small parameter”. Finally, we use combined homotopy perturbation method and Green’s function method for solving second order problems. Some examples are given to illustrate the effectiveness of methods. The results show that these methods provides a powerful mathematical tools for solving problems.
Creativity at the Crossroad Creative Education as Moral Education?  [PDF]
Sara Nosari
Creative Education (CE) , 2012, DOI: 10.4236/ce.2012.37B015

The man’s action, thanks to its creative capacities, gave a new order to the reality: the “created reality” does not present simply a different order, but is an authentic transformation. Which criteria had directed this transformation? Which will be the criteria of future transformation? The paper presents two possible ideas about creativity and argues in favor of a creative action educated and directed by an ethical criteria.

Using Figurative Language to Assess the Stage of Acceptance of Learning Disability as a Springboard for Treatment of Students with Learning Disabilities  [PDF]
Sara Givon
Creative Education (CE) , 2013, DOI: 10.4236/ce.2013.46054

In order to examine the emotional and cognitive processes experienced by adolescents with learning disabilities (LD), twenty tenth grade Israeli students were studied over three years. Data gathered through in-depth interviews underwent an axial-coding process, and a grounded theory model was constructed. The findings revealed various coping styles adopted by students throughout the process of accepting the disability. Participants were asked to use figurative language to describe their method of coping with the disability. Participants’ choice of phrase, metaphor or image characterized the phase of their acceptance as well as their coping style. This can be served as an effective tool of detection. Identifying the stage of students’ acceptance and their coping style may promote optimal treatment for students with LD.

Efeito do vírus do mosaico do trigo sobre o rendimento de trigo e triticale
Fitopatologia Brasileira , 2002, DOI: 10.1590/S0100-41582002000100008
Abstract: soil-borne wheat mosaic virus (sbwmv) is transmitted by the soil borne fungus polymyxa graminis and is responsible for an important virus disease on wheat (triticum aestivum). in order to evaluate the yield reduction in wheat due to sbwmv and in triticale, an experiment was carried out in naturally infested soil using wheat cultivars br 32, br 23, embrapa 120, or1, iac 5-maringá, embrapa 27, embrapa 16 and triticale cultivars (triticum secale) embrapa 53 and iapar 23. seeds were sown at an experimental farm of the "embrapa trigo". the plant height, the number of tillers, the number of grains per spike, number of grains per plant, grain weight and thousand grain weight were evaluated. the data were submitted to analysis of variance, comparing the average/medium with the scott & knott at 5% of probability. a reduction height of plants up to 27.5% was observed on the 'iac 5-maringá'. the number of tillers, in 'br 32' showed a reduction of 25% in the symptomatic plants, while 'or 1' increased the number of tillers in 32.4% under the same conditions. the weight reduction of grain per plant varied from seven to 56% in wheat and from 51 to 59% in triticale. the thousand-grain weight varied from four to 26% in wheat and from 23 to 30% in triticale.
Influence of shade and irradiation time on the hardness of composite resins
Della Bona, álvaro;Rosa, Vinícius;Cecchetti, Dileta;
Brazilian Dental Journal , 2007, DOI: 10.1590/S0103-64402007000300010
Abstract: this study tested the following hypotheses: 1. increasing light irradiation time (it) produces greater values of superficial hardness on different depths (0 and 3 mm); and 2. a dark shade composite (a3) needs longer it than a light shade composite (a1) to produce similar hardness. disk-shaped specimens (n=24 per shade) were fabricated using a 3-mm-thick increment of composite resin (z100). specimens were randomly assigned to 3 groups (n=8) according to the it (400 mw/cm2) at the upper (u) surface: a1-10 and a3-10: 10 s; a1-20 and a3-20: 20 s; a1-40 and a3-40: 40 s. specimens were stored in black lightproof containers at 37oc for 24 h before indentation in a hardness tester. three vickers indentations were performed on the u and lower (l) surfaces of each specimen. the indent diagonals were measured and the hardness value calculated. the results were analyzed statistically by anova and tukey's test (a=0.05). statistically significant differences were found between u and l surfaces of each composite shade-it combination (p=0.0001) and among the its of same shade-surface combination (p=0.0001), except between groups a1-20u and a1-40u, confirming the study hypothesis 1 and partially rejecting the hypothesis 2.
Flexural and diametral tensile strength of composite resins
Della Bona, álvaro;Benetti, Paula;Borba, Márcia;Cecchetti, Dileta;
Brazilian Oral Research , 2008, DOI: 10.1590/S1806-83242008000100015
Abstract: this study evaluated the flexural strength (sf) and the diametral tensile strength (st) of light-cured composite resins, testing the hypothesis that there is a positive relation between these properties. twenty specimens were fabricated for each material (filtek z250- 3m-espe; am- amelogen, ultradent; ve- vit-l-escence, ultradent; ex- esthet-x, dentsply/caulk), following iso 4049 and ansi/ada 27 specifications and the manufacturers? instructions. for the st test, cylindrical shaped (4 mm x 6 mm) specimens (n = 10) were placed with their long axes perpendicular to the applied compressive load at a crosshead speed of 1.0 mm/min. the sf was measured using the 3-point bending test, in which bar shaped specimens (n = 10) were tested at a crosshead speed of 0.5 mm/min. both tests were performed in a universal testing machine (emic 2000) recording the fracture load (n). strength values (mpa) were calculated and statistically analyzed by anova and tukey (a = 0.05). the mean and standard deviation values (mpa) were z250-45.06 ± 5.7; am-35.61 ± 5.4; ve-34.45 ± 7.8; and ex-42.87 ± 6.6 for st; and z250-126.52 ± 3.3; am-87.75 ± 3.8; ve-104.66 ± 4.4; and ex-119.48 ± 2.1 for sf. ex and z250 showed higher st and sf values than the other materials evaluated (p < 0.05), which followed a decreasing trend of mean values. the results confirmed the study hypothesis, showing a positive relation between the material properties examined.
Flexural strength and hardness of direct and indirect composites
Borba, Márcia;Della Bona, álvaro;Cecchetti, Dileta;
Brazilian Oral Research , 2009, DOI: 10.1590/S1806-83242009000100002
Abstract: the objective of this study was to evaluate the flexural strength (σf) and hardness (h) of direct and indirect composites, testing the hypotheses that direct resin composites produce higher σf and h values than indirect composites and that these properties are positively related. ten bar-shaped specimens (25 mm x 2 mm x 2 mm) were fabricated for each direct [d250 - filtek z250 (3m-espe) and d350 - filtek z350 (3m-espe)] and indirect [isin - sinfony (3m-espe) and ivm - vitavm lc (vita zahnfabrik)] materials, according to the manufacturer's instructions and iso4049 specifications. the σf was tested in three-point bending using a universal testing machine (emic dl 2000) at a crosshead speed of 0.5 mm/min (iso4049). knoop hardness (h) was measured on the specimens' fragments resultant from the σf test and calculated as h = 14.2p/l2, where p is the applied load (0.1 kg; dwell time = 15 s) and l is the longest diagonal of the diamond shaped indent (astm e384). the data were statistically analyzed using anova and tukey tests (α = 0.05). the mean σf and standard deviation values (mpa) and statistical grouping were: d250 - 135.4 ± 17.6a; d350 - 123.7 ± 11.1b; isin - 98.4 ± 6.4c; ivm - 73.1 ± 4.9d. the mean h and standard deviation values (kg/mm2) and statistical grouping were: d250 - 98.12 ± 1.8a; d350 - 86.5 ± 1.9b; isin - 28.3 ± 0.9c; ivm - 30.8 ± 1.0c. the direct composite systems examined produce higher mean σf and h values than the indirect composites, and the mean values of these properties were positively correlated (r = 0.91), confirming the study hypotheses.
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