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Search Results: 1 - 10 of 481886 matches for " Isaac A Chang "
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Thermal modeling of lesion growth with radiofrequency ablation devices
Isaac A Chang, Uyen D Nguyen
BioMedical Engineering OnLine , 2004, DOI: 10.1186/1475-925x-3-27
Abstract: We present an axisymmetric two-dimensional finite element model that calculates cell damage in tissues and compare lesion sizes using common tissue damage and iso-temperature contour definitions. The model accounts for both temperature-dependent changes in the electrical conductivity of tissue as well as tissue damage-dependent changes in local tissue perfusion. The data is validated using excised porcine liver tissues.The data demonstrate the size of thermal lesions is grossly overestimated when calculated using traditional temperature isocontours of 42°C and 47°C. The computational model results predicted lesion dimensions that were within 5% of the experimental measurements.When modeling radiofrequency ablation problems, temperature isotherms may not be representative of actual tissue damage patterns.The mitigation of primary and metastatic tumors by radiofrequency ablation is a developing research area. The goal of ablation is to necrose treatment volumes by raising the temperature of targeted tissues. Ablation probes are inserted percutaneously, laparoscopically, or during surgery into cancerous tumors. Once positioned, high frequency alternating current (450–550 kHz) is delivered through an uninsulated electrode into the surrounding tissues to a dispersive ground pad that is applied to the patient. The electromagnetic energy is converted to heat by resistive heating.While the usage of radiofrequency ablation devices is well established, efforts to optimize treatment strategies are ongoing. An important consideration in optimizing ablation is determining what treatment volumes are necessary and acceptable. In liver ablation, for example, treatment volumes generally extend a centimeter beyond the dimensions of a tumor [1-3]. Since the liver possesses regenerative characteristics, it is more critical to insure that necrosis is achieved in 100% of the cancerous cell volume than to minimize damage to healthy tissues. In contrast, a centimeter margin in cardiac abla
Review of "RF/Microwave Interaction with Biological Tissues" by André Vander Vorst, Arye Rosen, and Youji Kotsuka
Isaac Chang
BioMedical Engineering OnLine , 2006, DOI: 10.1186/1475-925x-5-50
Abstract: The book is organized into six chapters. Chapter 1: Fundamentals in Electromagnetics provides a summary of the basic electromagnetics as it applies to biological tissues. Unlike traditional texts on electromagnetics, this chapter presents the major theoretical points as "observations." The chapter mainly focuses on the relationship between field quantities and the description of static/dynamic movement of charge. The chapter also focuses on the penetration of fields in biological tissues, the description and plotting techniques for plotting complex admittance (i.e. Cole-Cole), the effects of fields in the near field, blackbody radiation, and microwave measurement techniques.Chapter 2: RF/Microwave Interaction Mechanisms in Biological Materials is a collection of sub-topics that largely describe the mechanisms that occur when fields interact with tissues. Sub-topics such as polarization and relaxation are introduced. Descriptions of conductivity and permittivity, and typical values measured in various tissues are presented. The chapter ends with a description of the fundamentals of thermodynamics and a discussion of energy and entropy.Chapter 3: Biological Effects presents a description of the methods and metrics used to describe exposure of RF/Microwave energy to biological tissues. The first part of the chapter focuses on a description of the specific absorption rate (SAR) and thermal distribution formulations. It introduces the reader to SAR limits for different biological tissues. The chapter then focuses on the published effects of RF fields on the nervous system, the brain and spinal cord, the blood-brain barrier, and cell and membranes. The chapter finishes by presenting experimental and computational methods for assessing SAR in tissues.Chapter 4: Thermal Therapy presents an extensive description of the different modes of RF heating. It focuses mainly on dielectric and inductive heating. Both the description of dielectric heating (from electric fields) and in
Finite Element Analysis of Hepatic Radiofrequency Ablation Probes using Temperature-Dependent Electrical Conductivity
Isaac Chang
BioMedical Engineering OnLine , 2003, DOI: 10.1186/1475-925x-2-12
Abstract: The results of four finite element models are compared: constant electrical conductivity without tissue perfusion, temperature-dependent conductivity without tissue perfusion, constant electrical conductivity with tissue perfusion, and temperature-dependent conductivity with tissue perfusion.The data demonstrate that significant errors are generated when constant electrical conductivity is assumed in coupled electrical-heat transfer problems that operate at high temperatures. These errors appear to be closely related to the temperature at which the ablation device operates and not to the amount of power applied by the device or the state of tissue perfusion.Accounting for temperature-dependent phenomena may be critically important in the safe operation of radiofrequency ablation device that operate near 100°C.The term "radiofrequency ablation probe" refers to a class of medical devices operating between 460–550 kHz that deliver therapeutic energy into soft tissues. The intent of these devices is to thermally necrose tissue by raising targeted tissue temperatures to approximately 100°C for a period of 10–15 minutes [1,2]. Ablation probes are inserted percutaneously or subdermally into tissues where cancerous tumors have been identified. Once the probes are positioned, radiofrequency energy is delivered through the probe, into surrounding tissue, and to an electrical ground pad that is applied to the skin of the patient.As a technique, the use of radiofrequency energy in ablation procedures has been well established. However, its use in treating tumors in soft organs, such as the liver, presents some new constraints that were not common to its previous uses. In cardiac ablation, for example, the goal of the ablation procedure is to eradicate the tissue pathology needed to sustain an arrhythmia, or abnormal heart rhythm [3,4]. By monitoring changes in shape of the electrograms, physicians can determine when procedures are complete. In contrast, the absence of a natural
An Assessment of Heavy-Metal Contamination in Soils within Auto-Mechanic Workshops Using Enrichment and Contamination Factors with Geoaccumulation Indexes  [PDF]
Isaac A. Ololade
Journal of Environmental Protection (JEP) , 2014, DOI: 10.4236/jep.2014.511098
Abstract:

Soil characterization and heavy metals in different layers (0 - 15 cm; 15 - 30 cm and 30 - 45 cm depth) of automobile mechanic waste dumps were studied. The soils showed remarkably high levels of all the metals above background concentrations with most (Ni, Cu, Fe, Cr and Cd) decreasing with soil depth. The distribution pattern were in the following order Fe > Cu > Zn > Pb > Cr > Ni > Cd. Across all the sampling locations and profiles, Fe and Cd showed the highest (476.4 μg·g-1) and least (37.5 μg·g-1) mean concentrations respectively. Pollution load index (PLI) and index of geoaccumulation (Igeo) revealed overall high and moderate contamination respectively but the enrichment factors (EFs) for Pb Ni and Cd are severe. The inter-element relationship revealed the identical source of elements in the soils of the studied area. The accuracy of the results has been cheeked using the standard reference material; SRM (PACS-2). The mechanic waste dumps represent potential sources of heavy metal pollution to environment. The elevated levels of heavy metals in these soil profiles constitute a serious threat to both surface and groundwater.

Deconstructing the Glass Ceiling  [PDF]
Carol A. Isaac, Anna Kaatz, Molly Carnes
Sociology Mind (SM) , 2012, DOI: 10.4236/sm.2012.21011
Abstract: Aims: There is a large body of evidence-based research illustrating the challenges faced by women who strive in male-typed careers. The purpose of this paper is to outline and integrate a review of the relevant social psychology research into a model of women’s leadership. Proposed Conceptual Argument: As leadership is stereotypically a masculine dimension, women who emulate agentic characteristics will rise into leadership. However, empirical evidence overwhelmingly illustrates the consequences to agentic women whose competence is simultaneously expected and minimized. Findings/Conclusions: This model raises awareness of complex issues in research for women including: the “promotion of ‘male’ females”, “success does not equal competence”, “agentic women sustain reactive opposition”, “the process of self-selection”, “stereotypic threat”, and “equality equals greed”. Because of the ubiquity of these cognitive distortions, awareness may mitigate antagonism and conflict to propel women into leadership roles.
Proliferation of Microorganisms in Acidic Fermentation of Elaeis guineensis L. Waste  [PDF]
M. Adedolapo Orimoloye, A. Isaac Sanusi
Advances in Microbiology (AiM) , 2016, DOI: 10.4236/aim.2016.69063
Abstract: An investigation into the type of fermentation oil palm fruit waste undergoes and the probable microorganisms involved within a short period was carried out using simple fermenter. The temperature was determined using mercury thermometer, the pH of the medium was monitored with calibrated pH meter and the titratable acidic was determined using standard technique. The microbial profile of the medium was also evaluated using standard procedures. The highest temperature value was observed at day 0 (32.65°C) and the lowest at day 1 (29.50°C). The pH values of the fermentation oil palm fruit waste ranged between 4.15 - 4.60. The highest pH value was obtained at day 3 of the fermentation which was 4.60. The titratable acidity showed variation from day 0 - 2 and then with a continuous decrease till day 5. The least titratable acidity was obtained at day 5 (0.03) and the highest at day 2 (0.77). Bacteria load decreases from 1.0 × 108 - 1.6 × 107 cfu/ml, while the fungi population increases from day 0 to day 5 of the fermentation period (1 × 103 - 2 × 104 sfu/ml). Bacterial isolates obtained were Micrococcus leteus, Proteus vulgaris, Bacillus cereus, Baccillus subtilis, and Staphylococcus aureus while the fungal isolates obtained were Aspergillus niger, Neurospora crassa, Brachysporium spp,
Relationships between Cadmium in Tissues of Cacao Trees and Soils in Plantations of Trinidad and Tobago  [PDF]
Gideon Ramtahal, Ivan Chang Yen, Isaac Bekele, Frances Bekele, Lawrence Wilson, Kamaldeo Maharaj, Lisa Harrynanan
Food and Nutrition Sciences (FNS) , 2016, DOI: 10.4236/fns.2016.71005
Abstract: The primary source of cadmium in cocoa beans has been linked to its direct uptake by the cacao plant from cadmium contaminated soils. This research was conducted to evaluate and interpret significant relationships between cadmium levels in tissues of the cacao plant and soils from cocoa-growing areas in Trinidad and Tobago. Total (HNO3-extractable) concentrations of cadmium in both tissues and soils were determined. The levels of cadmium measured varied in the order: leaves > pods > shells > nibs > soil. Cadmium levels in all the cacao tissues analyzed were significantly (p < 0.05), positively and strongly correlated with each other. Additionally, significant (p < 0.05) positive relationships were also identified between Cd in cacao tissues and corresponding total HNO3-extractable Cd levels in soils. These findings suggest that they can possibly be used as predictive tools for assessing Cd levels in cacao.
Cutaneous markers in Ochronosis
Isaac Jebaraj,Rao A
Indian Journal of Medical Sciences , 2005,
Abstract:
Achilles tendon enthesopathy in ochronosis
Jebaraj Isaac,Rao A
Journal of Postgraduate Medicine , 2006,
Abstract:
On the Comparison of Microstructure Characteristics and Mechanical Properties of High Chromium White Iron with the Hadfield Austenitic Manganese Steel  [PDF]
Johnson O. Agunsoye, Talabi S. Isaac, Agbeleye A. Abiona
Journal of Minerals and Materials Characterization and Engineering (JMMCE) , 2013, DOI: 10.4236/jmmce.2013.11005
Abstract: In this study, high chromium white iron (HC-Wi) alloy and the Hadfield steel were studied. The microstructure of this high-chromium iron was studied using Metallurgical optical microscopy (OM) and compared to the Hadfield steel. The hardness and unnotched charpy impact strength of the HC-Wi alloy and Hadfield steel were examined at ambient temperature in the as-cast and heat-treated conditions. A pin-on-disc test at linear speed of 1.18 m/s and a 10 N normal load was employed to evaluate the wear behavior of both steel samples. Microstructural results showed that varying the carbon level in HC-Wi alloys can affect the chromium carbide morphology and its distribution in the austenite matrix which leads to considerable changes of the mechanical properties. Abrasion test showed that HC-Wi alloys have superior wear resistance, about three times of the Hadfield steel.
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