High Performance Gear Obtained by Die Warm Compaction and Rapid Cooling Process

Calero J.A. 한국분말야금학회 2006 한국분말야금학회 학술대회논문집 Vol.2006 No.1

PM recent developments focus on increasing this technology's competitiveness when compared to wrought materials. Warm compaction allows the replacement of a double press double sinter process with a single warm press and sintering step, thus allowing cost and time savings. Moreover there are added benefits to consider such as reducing work in process and lessening part's logistics cost. This paper presents a successful industrial trial to replace a double press-double sinter process with a warm die compaction and sintering process. The part chosen was a high performance gear containing 0,9% wt. carbon. Sintering was conducted in a belt furnace at in a nitrogen rich atmosphere with rapid cooling process in order to obtain a quasi fully martensitic structure with a minimum of 700HV0,1 and 450HV10 after annealing. The balance between properties and cost is favoured by the use of a singular lubricant developed in a Eureka frame project together with POMETON S.A. and die warm compaction. Warm compaction is only needed to be effective on the gear teeth, in order to achieve the required properties. Therefore only the die is actually heated. This simplified system avoids flow rate problems typically involved when using more elaborate warm compaction equipments.

El problema del fracaso escolar y del abandono escolar prematuro en Espana

( Alvaro Choi Y Jorge Calero ) 고려대학교 스페인·라틴아메리카연구소 2010 스페인라틴아메리카연구 Vol.3 No.-

Uno de los principales problemas del sistema educativo espanol consiste en sus elevadas tasas de fracaso escolar y de abandono escolar prematuro, que duplican la media de la UE. Esta situacion tiene graves consecuencias para la insercion laboral y social del individuo y, a nivel global, supone un desaprovechamiento de recursos materiales y humanos, asi como un riesgo para la cohesion de la sociedad espanola. En este articulo se revisan algunas de las causas que provocan que un alumno corra el riesgo de no completar sus estudios obligatorios, algunas de sus consecuencias, y se efectuan propuestas de politica educativa para combatir el problema.

Private tutoring and academic achievement in Korea: An approach through PISA-2006

Álvaro Choi,Jorge Calero,Josep-Oriol Escardíbul 한국교육개발원 2012 KEDI Journal of Educational Policy Vol.9 No.2

Although not exclusive to the Republic of Korea’s educational system, the pervasiveness of private tutoring, and its consequences, serve to distinguish it from systems operated in other countries. This paper quantifies the impact of time spent on private tutoring on the performance of students in the three competence fields assessed in the Programme for International Student Assessment (PISA). Instrumental variables are applied in a multilevel framework to address endogeneity. Our results indicate that the impact of time dedicated to private tutoring on academic performance depends on the particular competence: positive for mathematics, positive but decreasing for reading, and non-significant for science.

Study of kinetics in the biosorption of lead onto native and chemically treated olive stone

G. Blazquez,M. Calero,A. Ronda,G. Tenorio,M.A. Martın-Lara 한국공업화학회 2014 Journal of Industrial and Engineering Chemistry Vol.20 No.5

In this research, olive stone was used as precursor for the development of new biosorbents for lead ions. Chemical treatments were analyzed in terms of their effects on physical–chemical properties and kinetics of lead removal. A kinetic study of the biosorption of lead ions by olive stone was analyzed according to six different kinetic models (pseudo first, pseudo second, pseudo n-order, Elovich, solid diffusion and double exponential models). The biosorption kinetic data were successfully described with pseudo-nth order and double exponential models for all biosorbents. The double exponential model allowed estimating the values of external and internal mass transfer coefficients. The values of external mass transfer coefficient (ke) ranged from 42.62 10 6 to 508.3 10 6 m min 1 and the internal mass transfer coefficient (ki) from 3.76 10 6 to 73.4 10 6 m min 1. On the other hand, the analysis of experimental data showed that chemical treatments of the biomass led to increase biosorption capacity of the native biomass.

Copper biosorption by pine cone shell and thermal decomposition study of the exhausted biosorbent

G. Blazquez,M.A. Martın-Lara,E. Dionisio-Ruiz,G. Tenorio,M. Calero 한국공업화학회 2012 Journal of Industrial and Engineering Chemistry Vol.18 No.5

Pine cone shell (PCS), a vegetable solid waste has been used as effective and efficient biosorbent for the removal of Cu(II) from aqueous solutions. The biosorbent was characterized by elemental analysis,potentiometric titrations, surface area and pore size distribution and FTIR analyses. Batch adsorption experiments were carried out as a function of solution pH, particle size, biosorbent dosage, contact time,and initial metal ion concentration. Then, equilibrium isotherms and kinetic data parameters were evaluated. Equilibrium data agreed well with Langmuir isotherm model. The biosorption capacities of PCS for Cu(II) were determined at 25 8C with the Langmuir model as 6.81 mg/g. The kinetics data fitted well into the pseudo-second-order model with correlation coefficient greater than 0.99. Also, dynamic biosorption studies were carried out using a packed-bed column and the main column parameters were determined. Pine cone shell was shown to be a promising biosorbent for Cu(II) removal from aqueous solutions. Finally, the pyrolysis characteristics of native PCS and Cu-loaded PCS were investigated by thermogravimetric analysis (TGA) in order to study the possible recycling of PCS after its use as biosorbent of copper.

Multiple biosorption–desorption cycles in a fixed-bed column for Pb(II) removal by acid-treated olive stone

M.A. Martın-Lara,G. Blazquez,A. Ronda,I.L. Rodrıguez,M. Calero 한국공업화학회 2012 Journal of Industrial and Engineering Chemistry Vol.18 No.3

Biosorption of Pb2+ from aqueous solutions and desorption of Pb2+ from acid-treated olive stone were studied. Equilibrium screening tests of lead desorption established a solution of 0.3 M hydrochloric acid as the most appropriate eluting agent. Fixed-bed biosorption and desorption recovery curves for Pb2+were obtained for multiple consecutive biosorption–desorption cycles and the biosorption properties of the biomass for Pb2+ were compared after each cycle to evaluate the stability of the biomass. The biosorbent retained most of its original uptake capacity over fourteen cycles of use. Life factor calculation revealed that biosorbent bed would be completely exhausted after 71.3 cycles.

Evaluation and comparison of the biosorption process of copper ions onto olive stone and pine bark

G. Blazquez,M.A. Martin-Lara,E. Dionisio-Ruiz,G. Tenorio,M. Calero 한국공업화학회 2011 Journal of Industrial and Engineering Chemistry Vol.17 No.6

Olive stone (OS) and pine bark (PB) were used as effective biosorbents for the removal of Cu(II) from aqueous solutions. The biosorbents were characterized by elemental analysis, potentiometric titrations,surface area and pore size distribution and FTIR analyses. Batch adsorption experiments were carried out as a function of pH, particle size, biosorbent dosage, contact time and initial copper concentration. Equilibrium data agreed well with Langmuir isotherm. The kinetics data fitted well into the pseudosecond-order model with correlation coefficient greater than 0.99. Finally, dynamic biosorption studies were carried out using a packed bed column and the main column parameters were determined.

E2E Network Slice Management Framework for 5G Multi-tenant Networks

Chirivella-Perez, Enrique Chirivella,Salva-Garcia, Pablo,Sanchez-Navarro, Ignacio,Alcaraz-Calero, Jose,Wang, Qi 한국통신학회 2023 Journal of communications and networks Vol.25 No.3

Network slicing is one of the cornerstone featuresof the fifth generation (5G) networks to enable the multiplexingof virtualised logical networks over the same physical networkinfrastructure for various vertical business services. Architecturesbased on network slicing enable network operators to offer end-to-end (E2E) vertical services whilst assuring fulfilling tailoredservice level agreement (SLA) requirements. Despite the numer-ous benefits that this concept offers, the need for efficient, scalableand holistic E2E management of network slicing significantlycomplicates network operators’ network management and im-poses significant challenges in the quality of service (QoS). Thispaper proposes a novel intent-based slice manager frameworkover a service base 5G architecture that allows flexible definitionsto customise network slices, automates all essential managementtasks for 5G network slice providers, manages the life cycles ofall sorts of network slices, and guarantees their QoS in a unifiednetwork slice management framework. The proposed frameworkis empirically validated in a realistic large-scale 5G multi-tenantinfrastructure. The high scalability of the framework is basedon the empirical results supporting more than 512 physicalmachines, 534288 virtual machines and more than two millionnetwork interfaces.

Total Transit Time and Probiotic Persistence in Healthy Adults: A Pilot Study

Annie Tremblay,Jeremie Auger,Zainab Alyousif,Sara E Caballero Calero,Olivier Mathieu,Daniela Rivero-Mendoza,Amal Elmaoui,Wendy J Dahl,Thomas A Tompkins 대한소화기 기능성질환∙운동학회 2023 Journal of Neurogastroenterology and Motility (JNM Vol.29 No.2

Background/AimsMotility, stool characteristics, and microbiota composition are expected to modulate probiotics’ passage through the gut but their effects on persistence after intake cessation remain uncharacterized. This pilot, open-label study aims at characterizing probiotic fecal detection parameters (onset, persistence, and duration) and their relationship with whole gut transit time (WGTT). Correlations with fecal microbiota composition are also explored. MethodsThirty healthy adults (30.4 ± 13.3 years) received a probiotic (30 × 109 CFU/capsule/day, 2 weeks; containing Lactobacillus helveticus R0052, Lacticaseibacillus paracasei HA-108, Bifidobacterium breve HA-129, Bifidobacterium longum R0175, and Streptococcus thermophilus HA-110). Probiotic intake was flanked by 4-week washout periods, with 18 stool collections throughout the study. WGTT was measured using 80% recovery of radio-opaque markers. ResultsTested strains were detected in feces ~1-2 days after first intake and persistence after intake cessation was not significantly different for R0052, HA-108, and HA-129 (~3-6 days). We identified 3 WGTT subgroups within this population (named Fast, Intermediate, and Slow), which could be classified by machine learning with high accuracy based on differentially abundant taxa. On average, R0175 persisted significantly longer in the intermediate WGTT subgroup (~8.5 days), which was mainly due to 6 of the 13 Intermediate participants for whom R0175 persisted ≥ 15 days. Machine learning classified these 13 participants according to their WGTT cluster (≥ 15 days or < 5 days) with high accuracy, highlighting differentially abundant taxa potentially associated with R0175 persistence. ConclusionThese results support the notion that host-specific parameters such as WGTT and microbiota composition should be considered when designing studies involving probiotics, especially for the optimization of washout duration in crossover studies but also for the definition of enrollment criteria or supplementation regimen in specific populations.

Core Decompression Combined with Implantation of Autologous Bone Marrow Concentrate with Tricalcium Phosphate Does Not Prevent Radiographic Progression in Early Stage Osteonecrosis of the Hip

Hernandez Alejandro,Nuñez Jorge H.,Sallent Andrea,Gargallo-Margarit Albert,Gallardo-Calero Irene,Barro Victor 대한정형외과학회 2020 Clinics in Orthopedic Surgery Vol.12 No.2

Background: Untreated osteonecrosis of the femoral head ultimately leads to secondary coxarthrosis. The aim of this study was to determinate if the core decompression of the femoral head combined with implantation of autologous bone marrow concentrate with tricalcium phosphate could be used to prevent radiographic progression of early stage osteonecrosis of the hip. We also sought to determine whether this treatment improved clinical outcomes and reduced the need for total hip arthroplasty. Methods: Eighteen hips were included in the present study. All of them underwent core decompression of the femoral head combined with implantation of autologous bone marrow concentrate with tricalcium phosphate between 2007 and 2012. The cell concentrate was obtained from the posterior iliac crest and processed and implanted during the same surgical procedure. Patient demographic data, clinical data including modified Harris hip score, and radiological data were collected preoperatively, postoperatively, and during the follow-up period. Also, survival endpoints were analyzed: time of femoral head collapse and need for total hip arthroplasty. Results: The mean age of patients was 37.8 years (standard deviation [SD], 9.31 years). The mean follow-up was 68.9 months (SD, 15.0 months). In most cases (70.6%), the etiology of the osteonecrosis of the femoral head was corticosteroid use; in the remaining cases, secondary to alcohol use. Core decompression of the femoral head combined with implantation of autologous bone marrow concentrate with tricalcium phosphate did not prevent progression to collapse (< 80% at 5 years) although modified Harris hip scores improved. Overall median survival with the total hip arthroplasty as endpoint was 23 months (95% confidence interval [CI], 14.9 to 31.1 months). Overall median survival time with any degree of collapse as endpoint was 7 months (95% CI, 2.0 to 12.0 months). Conclusions: The results obtained in this study suggest that core decompression combined with implantation of autologous bone marrow concentrate and tricalcium phosphate will not prevent radiographic progression of early stage osteonecrosis of the hip. These finding also suggest that the absence of indications for hip replacement alone is not an indicator of good response to the treatment, and it is important to note the radiological results.