Study of Dynamic Behaviors in a Spin Valve System Modeled by the Landau-Lifshitz-Slonczewski Equation

Javier A. Velez,Edward Mosso,Omar J. Suarez 한국자기학회 2019 Journal of Magnetics Vol.24 No.3

In this work, the dynamic behavior of a spin valve oscillator with a Nickel-free layer, modeled by the Landau-Lifshitz-Slonczewski equation is studied. It is considered a constant applied field and a spin current with two components, a constant term and a term with a time-dependent harmonic modulation. Techniques to characterize dynamic behaviors of systems, such as Lyapunov exponents, bifurcation diagram, phase portraits, time series, and Fourier spectra were used. It is demonstrated that the system presents multiple transitions between chaotic and regular states when the constant magnetic field, the magnitude, and frequency of the alternating current are varied. Furthermore, it is found that the effect of the magnetic field and the amplitude of the currents play a meaningful role in the chaotic behavior start.

Treatment Response Assessment of Skeletal Metastases in Prostate Cancer with 18F-NaF PET/CT

Erik M. Velez,Bhushan Desai,Hossein Jadvar 대한핵의학회 2019 핵의학 분자영상 Vol.53 No.4

Purpose To determine the utility of 18F-sodium fluoride positron emission tomography-computed tomography (18F-NaF PET/ CT) in the imaging assessment of therapy response in men with osseous-only metastatic prostate cancer. Methods In this Institutional Review Board–approved single institution retrospective investigation, we evaluated 21 18F-NaF PET/CTscans performed in 14 patients with osseous metastatic disease from prostate cancer and no evidence of locally recurrent or soft-tissue metastatic disease who received chemohormonal therapy. Imaging-based qualitative and semi-quantitative parameters were defined and compared with changes in serum PSA level. Results Qualitative and semi-quantitative image-based assessments demonstrated > 80% concordance with good correlation (SUVmax κ = 0.71, SUVavg κ = 0.62, SUVsum κ = 0.62). Moderate correlation (κ = 0.43) was found between SUVmax and PSA-based treatment response assessments. There was no statistically significant correlation between PSA-based disease progression and semi-quantitative parameters. Qualitative imaging assessment was moderately correlated (κ = 0.52) with PSA in distinguishing responders and non-responders. Conclusion 18F-NaF PET/CT is complementary to biochemical monitoring in patients with bone-only metastases from prostate cancer which can be helpful in subsequent treatment management decisions.

Effects of Food Price on Food Security and Poverty in Latin America: A Shapley Decomposition Approach

( Maria Daniela C. Velez ),( Jae Bong Chang ) 한국농업경제학회 2020 農業經濟硏究 Vol.61 No.4

As it is the poor households known to spend over 50% of their budget share on food, which is a risk of falling back into poverty as a result of food price changes. Thus, this research aims to determine aside from what factors contributed to food price and non-food price changes across countries in Latin America; how increases in food price could undermine the progress achieved in poverty reduction by assessing food and non-food expenditure of low income households of two lower-income, two upper-middle income and two higher income countries in Latin America. Using Shapley’s Value Decomposition to evaluate food expenditure to estimate each components effect (food price, non-food price and income) on aggregate poverty in Bolivia, Chile, Colombia, Ecuador, Honduras and Uruguay. When food and non-food inflation can influence the level of purchasing power and therefore each individual household’s economic means (real income) to acquire the food requirements needed to attain their optimum level of growth. We found that food and non-food consumption are more inelastic for Honduras and Uruguay, while more elastic for Ecuador and Chile. In terms of the estimated poverty impact, we found that poverty headcount rates increased in all the six economies observed, with a varying poverty condition across the six countries analyzed; the highest poverty headcount ratios have being obtained for Colombia, followed by Uruguay and Chile. Whereas, the lowest poverty headcount ratios were registered for Bolivia, Ecuador, and Honduras.

Dengue virus serological prevalence and seroconversion rates in children and adults in Medellin, Colombia: implications for vaccine introduction

Carabali, Mabel,Lim, Jacqueline Kyungah,Velez, Diana Carolina,Trujillo, Andrea,Egurrola, Jorge,Lee, Kang Sung,Kaufman, Jay S.,DaSilva, Luiz Jacinto,Velez, Ivan Dario,Osorio, Jorge E. Elsevier 2017 INTERNATIONAL JOURNAL OF INFECTIOUS DISEASES Vol.58 No.-

<▼1><P><B>Highlights</B></P><P>•<P>A total of 3684 individuals between 1 and 65 years old participated in the survey.</P>•<P>The overall seroprevalence by IgG Indirect ELISA was 61%.</P>•<P>The overall seroconversion rate was 8.7% per 1000 person-months over 2.5 years.</P>•<P>The highest rate of infection was observed during the fifth visit (February 2014).</P></P></▼1><▼2><P><B>Summary</B></P><P><B>Background</B></P><P>Dengue is an important public health problem worldwide. A vaccine has recently been licensed in some countries of Latin America and Asia. Recommendations for dengue vaccine introduction include endemicity and a high serological prevalence of dengue in the territories considering its introduction.</P><P><B>Methods</B></P><P>A community-based survey was conducted to estimate dengue seroprevalence and age-specific seroconversion rates in a community in Medellin, Colombia, using a dengue serological test (IgG indirect ELISA). Residents were selected at random and were first screened for dengue infection; they were then followed over 2.5 years.</P><P><B>Results</B></P><P>A total of 3684 individuals aged between 1 and 65 years participated in at least one survey. The overall dengue seroprevalence was 61%, and only 3.3% of seropositive subjects self-reported a past history of dengue. Among dengue virus (DENV)-naïve subjects with more than two visits (<I>n</I> = 1002), the overall seroconversion rate was 8.7% (95% confidence interval 7.3–10.4) per 1000 person-months, over the study period. Overall, the mean age of DENV prevalent subjects was significantly higher than the mean age of seroconverted subjects. Specifically, DENV seropositivity over 70% was observed in participants over 21 years old. Serotype-specific plaque-reduction neutralization tests (PRNT) revealed that all four dengue serotypes were circulating, with DENV4 being most prevalent.</P><P><B>Conclusions</B></P><P>These laboratory-based findings could inform dengue vaccine decisions, as they provide age-specific seroprevalence and seroconversion data, evidencing permanent and ongoing dengue transmission in the study area. This study provides evidence for the existing rates of secondary and heterotypic responses, presenting a challenge that must be addressed adequately by the new vaccine candidates.</P></▼2>

외상성 뇌손상 후 전기자극을 활용한 치유 과정 촉진

박은영(E. Park),Johnathan G. Lyon(J. G. Lyon),Melissa Alvarado-Velez(M. Alvarado-Velez),Martha I. Betancur(M. I. Betancur),Nassir Mokarram(N. Mokarram),Ravi V. Bellamkonda(R. V. Bellamkonda),신현정(J. H. Sh Korean Society for Precision Engineering 2021 한국정밀공학회 학술발표대회 논문집 Vol.2021 No.5월

Constellation Design for Bit-Interleaved Coded Modulation (BICM) Systems in Advanced Broadcast Standards

[Institute of Electrical and Electronics Engineers 2017 IEEE transactions on broadcasting Vol.63 No.4

<P>This paper presents a generic methodology to optimize constellations based on their geometrical shaping for bit-interleaved coded modulation (BICM) systems. While the method can be applicable to any wireless standard design it has been tailored to two delivery scenarios typical of broadcast systems: 1) robust multimedia delivery and 2) UHDTV quality bitrate services. The design process is based on maximizing the BICM channel capacity for a given power constraint. The major contribution of this paper is a low complexity optimization algorithm for the design of optimal constellation schemes. The proposal consists of a set of initial conditions for a particle swarm optimization algorithm, and afterward, a customized post processing procedure for further improving the constellation alphabet. According to the broadcast application cases, the sizes of the constellations proposed range from 16 to 4096 symbols. The BICM channel capacities and performance of the designed constellations are compared to conventional quadrature amplitude modulation constellations for different application scenarios. The results show a significant improvement in terms of system performance and BICM channel capacities under additive white Gaussian noise and Rayleigh independently and identically distributed channel conditions.</P>

Capsule Endoscopy in Refractory Diarrhea-Predominant Irritable Bowel Syndrome and Functional Abdominal Pain

Manuel Valero,Gladys Bravo-Velez,Roberto Oleas,Miguel Puga-Tejada,Miguel Soria-Alcívar,Haydee Alvarado Escobar,Jorge Baquerizo-Burgos,Hannah Pitanga-Lukashok,Carlos Robles-Medranda 대한소화기내시경학회 2018 Clinical Endoscopy Vol.51 No.6

Background/Aims: Capsule endoscopy is a diagnostic method for evaluating the small bowel lumen and can detect undiagnosedlesions. The aim of this study was to evaluate the diagnostic yield and clinical impact of capsule endoscopy in patients with refractorydiarrhea-predominant irritable bowel syndrome and functional abdominal pain. Methods: This study involved a retrospective analysis of prospectively collected data, maintained in a database. Patients with refractorydiarrhea-predominant irritable bowel syndrome and functional abdominal pain within the period of March 2012 to March 2014 wereincluded. Capsule endoscopy was used to detect small bowel pathologies in both groups. Results: Sixty-five patients (53.8% female) fulfilled the inclusion criteria and had a mean (±standard deviation) age of 50.9±15.9 years. Clinically significant lesions were detected via capsule endoscopy in 32.5% of the patients in the abdominal pain group and 54.5% ofthe patients in the diarrhea group. Overall, 48% of patients had small bowel pathologies detected during the capsule endoscopy study. Inflammatory lesions and villous atrophy were the most frequent lesions identified in 16.9% and 15.3% of patients in the abdominalpain and the diarrhea groups, respectively. Conclusions: Routine use of capsule endoscopy in patients with irritable bowel syndrome should not be recommended. However, inpatients with refractory conditions, capsule endoscopy may identify abnormalities.

Numerical characterization of real railway overhead cables

Cristina Sanchez-Rebollo,Enrique Velez,Jesus R. Jimenez-Octavio 한국풍공학회 2015 Wind and Structures, An International Journal (WAS Vol.21 No.1

This paper presents a numerical characterization of real railway overhead cables based on computational fluid dynamics (CFD). Complete analysis of the aerodynamic coefficients of this type of cross section yields a more accurate modelling of pressure loads acting on moving cables than provided by current approaches used in design. Thus, the characterization of certain selected commercial cables is carried out in this work for different wind speeds and angles of attack. The aerodynamic lift and drag coefficients are herein determined for two different types of grooved cables, which establish a relevant data set for the railway industry. Finally, the influence of this characterization on the fluid-structure interaction (FSI) is proved, the static behavior of a catenary system is studied by means of the finite element method (FEM) in order to analyze the effect of different wind angles of attack on the stiffness distribution.

Numerical characterization of real railway overhead cables

Sanchez-Rebollo, Cristina,Velez, Enrique,Jimenez-Octavio, Jesus R. Techno-Press 2015 Wind and Structures, An International Journal (WAS Vol.21 No.1

This paper presents a numerical characterization of real railway overhead cables based on computational fluid dynamics (CFD). Complete analysis of the aerodynamic coefficients of this type of cross section yields a more accurate modelling of pressure loads acting on moving cables than provided by current approaches used in design. Thus, the characterization of certain selected commercial cables is carried out in this work for different wind speeds and angles of attack. The aerodynamic lift and drag coefficients are herein determined for two different types of grooved cables, which establish a relevant data set for the railway industry. Finally, the influence of this characterization on the fluid-structure interaction (FSI) is proved, the static behavior of a catenary system is studied by means of the finite element method (FEM) in order to analyze the effect of different wind angles of attack on the stiffness distribution.

Management Impact of 68Ga-DOTATATE PET/CT in Neuroendocrine Tumors

Redmond-Craig Anderson,Erik M. Velez,Bhushan Desai,Hossein Jadvar 대한핵의학회 2021 핵의학 분자영상 Vol.55 No.1

Purpose The goal of our retrospective single tertiary academic medical center investigation was to examine the added diagnostic value and clinical impact of 68Ga-DOTATATE PET/CT in the therapeutic management of patients with neuroendocrine tumors (NETs). Methods Imaging database was queried for all “PET-DOTATATE” examinations performed at our tertiary care academic institution usingMONTAGE™. The patient’s clinical history and recent prior imaging were reviewed. The additional diagnostic value and clinical management impact of 68Ga-DOTATATE were assessed through retrospective chart review. Results A total of 81 68Ga-DOTATATE PET/CT scans in 74 patients were found, and 11 patientswere excluded fromanalysis as they had no prior imaging available for comparison, with resultant analysis cohort of 63 patients. Six patients had 2 ormore 68Ga- DOTATATE PET/CT examinations. The most common primary diagnosis was undifferentiated NET (63.5%), followed by carcinoid (27.0%), paraganglioma (4.8%), insulinoma (3.2%), and pheochromocytoma (1.6%). The primary sites of disease from the most to the least common were the pancreas (36.5%), small bowel (22.2%), unknown primary (15.9%), lung (6.3%), large bowel (6.3%), and mesentery (4.8%), and other locations accounted for 7.9%. In patients who had prior imaging available for comparison, there were new lesions identified on 68Ga-DOTATATE PET/CT in 21 patients (33.3%) that were not identified on other prior imaging modalities. Of these patients, 5 underwent subsequentMRI and 1 had a repeat 68Ga-DOTATATE PET/CT to further characterize new lesions seen. Moreover, 15 patients (23.8%) had a change in treatment plan, including altering medical therapy in 9 patients, change in planned extent of surgical management in 5 patients, and cancelation of a planned primary tumor resection in 1 patient with metastatic disease. Conclusion Our retrospective cohort demonstrated that 68Ga-DOTATATE PET/CT improves lesion detection over conventional imaging in 33.3% and impacts the therapeutic management in 23.8% of patients with NET.