Characterization of Cure Kinetics and Physical Properties of a High Performance, Glass Fiber-Reinforced Epoxy Prepreg and a Novel Fluorine-Modified, Amine-Cured Commercial Epoxy.

Kinetic equation parameters for the curing reaction of a commercial glass fiber reinforced high performance epoxy prepreg composed of the tetrafunctional epoxy tetraglycidyl 4,4-diaminodiphenyl methane (TGDDM), the tetrafunctional amine curing agent 4,4'-diaminodiphenylsulfone (DDS) and an ionic initiator/accelerator, are determined by various thermal analysis techniques and the results compared. The reaction is monitored by heat generated determined by differential scanning calorimetry (DSC) and by high speed DSC when the reaction rate is high. The changes in physical properties indicating increasing conversion are followed by shifts in glass transition temperature determined by DSC, temperature-modulated DSC (TMDSC), step scan DSC and high speed DSC, thermomechanical (TMA) and dynamic mechanical (DMA) analysis and thermally stimulated depolarization (TSD). Changes in viscosity, also indicative of degree of conversion, are monitored by DMA. Thermal stability as a function of degree of cure is monitored by thermogravimetric analysis (TGA). The parameters of the general kinetic equations, including activation energy and rate constant, are explained and used to compare results of various techniques. The utilities of the kinetic descriptions are demonstrated in the construction of a useful time-temperature-transformation (TTT) diagram and a continuous heating transformation (CHT) diagram for rapid determination of processing parameters in the processing of prepregs. Shrinkage due to both resin consolidation and fiber rearrangement is measured as the linear expansion of the piston on a quartz dilatometry cell using TMA. The shrinkage of prepregs was determined to depend on the curing temperature, pressure applied and the fiber orientation. Chemical modification of an epoxy was done by mixing a fluorinated aromatic amine (aniline) with a standard aliphatic amine as a curing agent for a commercial Diglycidylether of Bisphenol-A (DGEBA) epoxy. The resulting cured network was tested for wear resistance using tribological techniques. Of the six anilines, 3-fluoroaniline and 4-fluoroaniline were determined to have lower wear than the unmodified epoxy, while the others showed much higher wear rates

Computer microvision measurements of stapedial motion in human temporal bone

Thesis (S.B. and M.Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1998.Includes bibliographical references (p. 79).by Bryan Clifford Bilyeu.S.B.and M.Eng

Dissemination of Endosulfan into the Environment

Organochlorine pesticide pollution of surface water, groundwater, soil, sediments, and air has been recognized as a major problem in many countries because of the persistence in different environments and the consequent potential adverse health effects. This report presents a review of literature on organochlorine insecticide of endosulfan, which has been used extensively for agricultural purposes. It summarizes information on nomenclature, physical-chemical properties, production, metabolism, degradation, distribution in the environment, toxicity, regulation, and technologies for the treatment of water and soil contaminated with this pesticide

Fast reduction of Cr(VI) from aqueous solutions using alumina

artículo ya publicadoHexavalent chromium is challenging to remove from industrial wastewater due the solubility and anionic nature of the chromates. Cr(VI) is typically removed by reduction to Cr(III), then precipitation or adsorption, which requires multiple steps and bulk reagents and generates sludge. In this project, we have evaluated a sintered alumina disk as a single step sorbent for Cr(VI). The disk was porous enough that 20 mL samples passed through in about 3 s using light suction. A single pass through the disk only reduced the [Cr(VI)] by 10–20%, but by passing the solution through the disk five times up to 80% was removed in samples up to 130 mg/L and up to around 50% for much higher concentrations. The five passes through the filter disk took less than a minute. On each pass through the disk the characteristic chromate UV–vis absorbance decreased, the Cr(VI) concentration (by the diphenylcarbazide method) decreased, and the pH rose slightly. The XRD pattern showed no change in the crystal structure of the alumina, but the SEM/EDS identified chromium on the surface. In addition to confirming chromium on the surface of the alumina, the XPS spectra showed a change in the binding energy of the aluminum, which is consistent with complexation. The system was fast and effective (in series), so should be applicable to industrial wastewater treatment.UAEMex, CONACy

Operations and Results from the 200 Gbps TBIRD Laser Communication Mission

Since launch in May 2022, the TeraByte Infrared Delivery (TBIRD) mission has successfully demonstrated 200 Gbps laser communications from a 6U CubeSat and has transferred up to 4.8 terabytes (TB) in a pass from low Earth orbit to ground. To our knowledge, this is the fastest downlink ever achieved from space. To support the narrow downlink beam required for high rate communications, the payload provides pointing feedback to the host spacecraft to precisely track the ground station throughout the 5-minute pass. The space and ground terminals utilize fiber-coupled coherent transceivers in conjunction with an automatic repeat request (ARQ) system to guarantee error-free communication through an atmospheric fading channel. This paper presents an overview of the link operations and mission results to date, as well as implications for future missions with high rate lasercom

NASA’s Terabyte Infrared Delivery (TBIRD) Program: Large-Volume Data Transfer from LEO

Satellites in low-Earth orbit (LEO) have on-board sensors that can generate large amounts of data to be delivered to a ground user. Direct-to-Earth delivery from LEO is challenging because of the sparse contact with a ground terminal, but the short link distances involved can enable very high data rates by exploiting the abundance of spectrum available at optical frequencies. We provide an overview and update of NASA’s Terabyte Infrared Delivery (TBIRD) program, which will demonstrate a direct-to-Earth laser communication link from a small satellite platform to a small ground terminal at burst rates up to 200Gbps. Such a link is capable of transferring several terabytes per day to a single ground terminal. The high burst rates are achieved by leveraging off-the-shelf fiber-telecommunications transceivers for use in space applications. A 2U TBIRD payload is currently being developed for flight on a 6U NASA CubeSat

Signal Transmission in the Auditory System

Contains table of contents for Section 3 and reports on four research projects.National Institutes of Health Grant R01 DC00194National Institutes of Health Grant P01 DC00119National Science Foundation Grant IBN 96-04642W.M. Keck Foundation Career Development ProfessorshipNational Institutes of Health Grant R01 DC00238Thomas and Gerd Perkins Award ProfessorshipAlfred P Sloan Foundation Instrumentation GrantJohn F. and Virginia B. Taplin Award in Health Sciences and TechnologyNational Institutes of Health/National Institute of Deafness and Other Communication DisordersNational Institutes of Health/National Institute of Deafness and Other Communication Disorders Grant PO1 DC0011

Cure Kinetics and Processing Parameters of Neat and Reinforced High Performance Epoxy Resins: Evaluation of Techniques

Kinetic equation parameters for the curing reaction of a commercial glass fiber reinforced high performance epoxy prepreg composed of the tetrafunctional epoxy tetraglycidyl 4,4-diaminodiphenyl methane (TGDDM), the tetrafunctional amine curing agent 4,4-diaminodiphenylsulfone (DDS) and an ionic initiator/accelerator, are determined by various thermal analysis techniques and the results compared. The reaction is monitored by heat generated determined by differential scanning calorimetry (DSC). The changes in physical properties indicating increasing conversion are followed by shifts in glass transition temperature determined by DSC and temperature-modulated DSC (TMDSC), thermomechanical (TMA) and dynamic mechanical (DMA) analysis and thermally stimulated depolarization (TSD). Changes in viscosity, also indicative of degree of conversion, are monitored by DMA. Thermal stability as a function of degree of cure is monitored by thermogravimetric analysis (TGA). The parameters of the general kinetic equations, including activation energy and rate constant, are explained and used to compare results of various techniques. The utilities of the kinetic descriptions are demonstrated in the construction of a useful time-temperature-transformation (TTT) diagram for rapid determination of processing parameters in the processing of prepregs. Copyright is held by the author, unless otherwise noted. All rights reserved. Files: Thesis.pdf Special Condition

Composition of Epoxy Resin, Aliphatic Amine Curing Agent and Halogenated Amine

Patent relating to the composition of epoxy resin, aliphatic amine curing agent and halogenated amine