Study of interfacial stiffness ratio of a rough surface in contact using a spring model

This study proposes the use of a simple spring model that relates the interfacial stiffness with the complex reflection coefficient of ultrasound in a rough contact. The spring model cannot be directly related to the real area of contact as this depends on the amount, shape and distribution of contacting asperities. However, it is clear that the model provides a non-destructive tool to easily evaluate both longitudinal and shear interfacial stiffnesses and their ratio. Experimental findings indicate that the interfacial stiffness ratio K-tau/K-sigma determined during loading/unloading cycles is sensitive to the roughness level and load hysteresis. The results deviate from the theoretical available micromechanical models, indicating that actual contacting phenomenon is more complex and other variables needed are not accounted for by the models. (C) 2009 Elsevier B.V. All rights reserved

Robotic-Assisted Laparoscopic “Salvage” Rectopexy for Recurrent Ileoanal J-Pouch Prolapse

Total restorative proctocolectomy with ileal pouch-anal anastomosis (RP/IPAA) has become the standard of care for the surgical treatment of ulcerative colitis. Despite its correlation with an excellent quality of life and favorable long-term outcomes, RP/IPAA has been associated with several complications. Prolapse of the ileoanal pouch is a rare and debilitating complication that should be considered in the differential diagnosis of pouch failure. Limited data exist regarding the prevalence and treatment of pouch prolapse. We present the case of a recurrent J-pouch prolapse treated with a novel minimally invasive “salvage” approach involving a robotic-assisted laparoscopic rectopexy with mesh

Using Factorial Design Methodology to Assess PLA-g-Ma and Henequen Microfibrillated Cellulose Content on the Mechanical Properties of Poly(lactic acid) Composites

In this work, a 22 factorial design was used to study the effect of microfibrillated henequen cellulose fibers (HENCEL) and PLA-g-MA coupling agent contents on the tensile, flexural, and impact mechanical properties and the heat deflection temperature (HDT) of biodegradable PLA composites. The results show that the principal effects of HENCEL and MA are statistically significant for the tensile, flexural, HDT, and impact strength properties of PLA composites. Regarding the interactions between the principle effects, MA-HENCEL, there are differences with respect to the mechanical property; for example, for tensile and flexural mechanical properties, there is a synergistic effect between MA and HENCEL, whereas for HDT and impact strength there is not any. The micromechanical analysis shows an excellent agreement between the measured and the estimated values for both the composite tensile strength and the elastic modulus and only slight deviations were noticed for high microfibrillated cellulose fibers content. The morphological analysis via SEM indicated that the addition of PLA-g-MA improved the fiber-matrix adhesion because of the HENCEL unbounding and pull-out decreases from the PLA matrix. The use of appropriate values of matrix strength and stiffness and considering the improved fiber-matrix adhesion of the coupling agent yield a good agreement between experimental and estimated values

Green Synthesis of Metallic and Carbon Nanostructures

The technological and biomedical applications of low toxicity and eco-friendly organic compounds are nowadays increasingly attracting the attention of researchers in nanoscience, who are aiming for more biocompatible and nanostructured systems for their application in antineoplastic therapies. This study presents the significance of “green components” in the production of graphene, metallic, and semiconductor nanoparticles, due to their antioxidant and antitumor properties. The formation of nanostructures is caused during green synthesis methods by organic molecules or carboxylic acid groups present in some plant extracts; for this reason, we include here a recapitulation and analysis of the role of carboxylic acids in those systems (organic). Furthermore, we propose the use of the extract from Opuntia ficus-indica cladodes to obtain metallic and carbon nanostructures, as an alternative biosynthesis method for the development of future nanobiotechnological applications

Auslander-Buchweitz approximation theory for triangulated categories

We introduce and develop an analogous of the Auslander-Buchweitz approximation theory (see \cite{AB}) in the context of triangulated categories, by using a version of relative homology in this setting. We also prove several results concerning relative homological algebra in a triangulated category \T, which are based on the behavior of certain subcategories under finiteness of resolutions and vanishing of Hom-spaces. For example: we establish the existence of preenvelopes (and precovers) in certain triangulated subcategories of \T. The results resemble various constructions and results of Auslander and Buchweitz, and are concentrated in exploring the structure of a triangulated category \T equipped with a pair (\X,\omega), where \X is closed under extensions and $\omega$ is a weak-cogenerator in \X, usually under additional conditions. This reduces, among other things, to the existence of distinguished triangles enjoying special properties, and the behavior of (suitably defined) (co)resolutions, projective or injective dimension of objects of \T and the formation of orthogonal subcategories. Finally, some relationships with the Rouquier's dimension in triangulated categories is discussed.Comment: To appear at: Appl. Categor. Struct. (2011); 22 page

Genetic and Molecular Characterization of Temperate and Tropical Forage Maize Inbred Lines

Livestock feeding in the Central highland of Mexico is based on harvest, grazing and annual forage conservation, with forage maize being the most important silage crop (Alarcón, 1995). Even though forage maize is extensively bred in Europe, USA and Asia since the 1900’s, this started in Mexico only in the 1960’s, and little is known about genetic diversity in both agronomic and nutritive value traits. Our breeding program goals are to analyze combining ability of biomass and quality predictors and to study the genetic relationship of inbred lines between lowland tropical and temperate races from Mesa Central, by genetic and molecular approaches

Learning curve for robotic-assisted laparoscopic colorectal surgery.

BACKGROUND: Robotic-assisted laparoscopic surgery (RALS) is evolving as an important surgical approach in the field of colorectal surgery. We aimed to evaluate the learning curve for RALS procedures involving resections of the rectum and rectosigmoid. METHODS: A series of 50 consecutive RALS procedures were performed between August 2008 and September 2009. Data were entered into a retrospective database and later abstracted for analysis. The surgical procedures included abdominoperineal resection (APR), anterior rectosigmoidectomy (AR), low anterior resection (LAR), and rectopexy (RP). Demographic data and intraoperative parameters including docking time (DT), surgeon console time (SCT), and total operative time (OT) were analyzed. The learning curve was evaluated using the cumulative sum (CUSUM) method. RESULTS: The procedures performed for 50 patients (54% male) included 25 AR (50%), 15 LAR (30%), 6 APR (12%), and 4 RP (8%). The mean age of the patients was 54.4 years, the mean BMI was 27.8 kg/m(2), and the median American Society of Anesthesiologists (ASA) classification was 2. The series had a mean DT of 14 min, a mean SCT of 115.1 min, and a mean OT of 246.1 min. The DT and SCT accounted for 6.3% and 46.8% of the OT, respectively. The SCT learning curve was analyzed. The CUSUM(SCT) learning curve was best modeled as a parabola, with equation CUSUM(SCT) in minutes equal to 0.73 × case number(2) - 31.54 × case number - 107.72 (R = 0.93). The learning curve consisted of three unique phases: phase 1 (the initial 15 cases), phase 2 (the middle 10 cases), and phase 3 (the subsequent cases). Phase 1 represented the initial learning curve, which spanned 15 cases. The phase 2 plateau represented increased competence with the robotic technology. Phase 3 was achieved after 25 cases and represented the mastery phase in which more challenging cases were managed. CONCLUSIONS: The three phases identified with CUSUM analysis of surgeon console time represented characteristic stages of the learning curve for robotic colorectal procedures. The data suggest that the learning phase was achieved after 15 to 25 cases

Genetic and Molecular Characterization of Temperate and Tropical Forage Maize Inbred Lines

The livestock feeding in the Central highland of Mexico is based on harvest, grazing and annual forage conservation, being forage maize the most important silage crop (Alarcón, 1995). Even though forage maize is extensively bred in Europe, USA and Asia since 1900\u27s, this started in Mexico in the 1960\u27s, and little is known about the genetic diversity in both agronomic and nutritive value traits. Our breeding program goals are to analyze combining ability of biomass and quality predictors and to study the genetic relationship of inbred lines between lowland tropical and temperate races from Mesa Central, by genetic and molecular approaches

Consequences of long-distance transport on the behavior and health of young-bulls that may affect their fitness to adapt to feedlots

Some studies have shown that long distance journeys and the type of trailer compartment have consequences on farm animal welfare. However, there is little evidence to indicate how these consequences affect the fitness of young bulls to adapt to a novel and challenging environment such as an intensive industrial feedlot. Therefore, the objective of our study was to evaluate the consequences of long-distance transport and trailer compartment on the behavior and health of young bulls during the first 60 days after arrival to the feedlot. An evaluation protocol was conducted to record individual behavior (scan sampling) and health indicators of young bulls from days 1-10 and 51-60 after arrival. In addition, three ocular thermal images were taken per animal in a chute during weighing, one each on day 0, day 2 (48 h) and day 50. From our results, the thermophysiological profile, maintenance behaviors and health indicators suggest that there are two distinct groups of consequences affecting animal fitness during the first two months in the feedlot. The first was linked to post-transport fatigue (PTF) that seemed to disappear after the 10 days post-arrival at feedlot. The second was related to signs of bovine respiratory disease (BRD) that began 6 days post-transport and persisted until day 60. In addition, the trailer compartments known as the belly and the deck were shown to be problematic for animal welfare, where the transport in the belly was linked to fatigue after transport, while transport in the deck was associated with respiratory problems. Our study underscores the importance of applying preconditioning practices in cow-calf rearing systems at least a couple of months prior to the long-distance journey, in addition to implementing good loading practices to select which animals are best suited for a given compartment. Our results may be useful to minimize the impacts of PTF and BRD, to propose best practices for livestock transport in countries with similar production systems and agroecosystems