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- Title
- REAL-TIME TRAFFIC SIGN RECOGNITION WITH RECONFIGURABLE HARDWARE
- Creator
- Waite, Sheldon
- Date
- 2012-07-12, 2012-07
- Description
-
This work describes an implementation of a system that recognizes tra c signs within an image or video frame. In addition it covers a brief...
Show moreThis work describes an implementation of a system that recognizes tra c signs within an image or video frame. In addition it covers a brief history of automotive technology and the safety motivations for the technology presented here. An algo- rithm is presented that takes RGB image data, extracts relevant pixels, lters the image, labels prospective tra c signs and evaluates them against template tra c sign images. Furthermore a system is described that uses a Virtex 5 Xilinx FPGA and the EDK tool kit to create an embedded processor and a hardware IP periph- eral that together implement the algorithm. This implementation is shown to have positive results both in terms of timing performance and accuracy.
M.S. in Computer Engineering, July 2012
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- Title
- DETECTING GNSS SPOOFING ATTACKS USING INS COUPLING
- Creator
- Tanil, Cagatay
- Date
- 2016, 2016-12
- Description
-
Vulnerability of Global Navigation Satellite Systems (GNSS) users to signal spoofing is a critical threat to positioning integrity, especially...
Show moreVulnerability of Global Navigation Satellite Systems (GNSS) users to signal spoofing is a critical threat to positioning integrity, especially in aviation applications, where the consequences are potentially catastrophic. In response, this research describes and evaluates a new approach to directly detect spoofing using integrated Inertial Navigation Systems (INS) and fault detection concepts based on integrity monitoring. The monitors developed here can be implemented into positioning systems using INS/GNSS integration via 1) tightly-coupled, 2) loosely-coupled, and 3) uncoupled schemes. New evaluation methods enable the statistical computation of integrity risk resulting from a worst-case spoofing attack – without needing to simulate an unmanageably large number of individual aircraft approaches. Integrity risk is an absolute measure of safety and a well-established metric in aircraft navigation. A novel closed-form solution to the worst-case time sequence of GNSS signals is derived to maximize the integrity risk for each monitor and used in the covariance analyses. This methodology tests the performance of the monitors against the most sophisticated spoofers, capable of tracking the aircraft position – for example, by means of remote tracking or onboard sensing. Another contribution is a comprehensive closed-loop model that encapsulates the vehicle and compensator (estimator and controller) dynamics. A sensitivity analysis uses this model to quantify the leveraging impact of the vehicle’s dynamic responses (e.g., to wind gusts, or to autopilot’s acceleration commands) on the monitor’s detection capability. The performance of the monitors is evaluated for two safety-critical terminal area navigation applications: 1) autonomous shipboard landing and 2) Boeing 747 (B747) landing assisted with Ground Based Augmentation Systems (GBAS). It is demonstrated that for both systems, the monitors are capable of meeting the most stringent precision approach and landing integrity requirements of the International Civil Aviation Organization (ICAO). The statistical evaluation methods developed here can be used as a baseline procedure in the Federal Aviation Administration’s (FAA) certification of spoof-free navigation systems. The final contribution is an investigation of INS sensor quality on detection performance. This determines the minimum sensor requirements to perform standalone GNSS positioning in general en route applications with guaranteed spoofing detection integrity.
Ph.D. in Mechanical and Aerospace Engineering, December 2016
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- Title
- Widget Applications to Enhance the Tru2Way Consumer Experience (sequence unknown), IPRO 312 - Deliverables: IPRO 312 Project Plan F09
- Creator
- Alsharief, Yagoob, Aulfata, Muluken, Curtis, Christopher, Dhewaju, Anusuya, Mooney, Kevin, Mutyaba, Kevin, Ndoping, Marco, Onaissi, Samah, Peterson, Naomi, Siwek, Steven, Wallace, Sean, Yi, Won-jae
- Date
- 2009-12
- Description
-
The IPRO teams objectives are to provide Comcast with feedback from an outside perspective, allowing them to see where their Tru2Way system...
Show moreThe IPRO teams objectives are to provide Comcast with feedback from an outside perspective, allowing them to see where their Tru2Way system needs additional attention or support.
Sponsorship: Comcast
Deliverables for IPRO 312: Widget Applications to Enhance the Tru2Way Consumer Experience for the fall 2009 semester
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- Title
- IMPACT OF THERMAL PROCESSING ON THE STRUCTURAL AND IMMUNOLOGICAL PROPERTIES OF MAJOR EGG AND MILK ALLERGENS
- Creator
- Chandra, Srinivasa Rao
- Date
- 2011-05-03, 2011-05
- Description
-
The underlying mechanism of food allergy is not well understood. Research has increasingly focused on the characterization of food allergens....
Show moreThe underlying mechanism of food allergy is not well understood. Research has increasingly focused on the characterization of food allergens. Since most foods are cooked prior to consumption, information relating to the impact of thermal processing on the properties of allergenic proteins is critical for allergen risk assessment. This study examined the impact of thermal processing on the structure and the antigenic potential of the major egg and milk allergens, ovomucoid (OVO) and -lactoglobulin (BLG) both A and B variants respectively. OVO and BLG were subjected to thermal processing under moist and dry heat conditions for 10 min. No significant changes in the solubility of both proteins were observed after boiling, autoclaving or dry heating up to 204C. At 232C, a significant protein loss was observed. Inhibition ELISA was used to determine the effect of heat treatment on the capacity of these proteins to bind rabbit derived IgG antibodies. While boiling and autoclaving caused a decrease in IgG binding of OVO, an increase in IgG binding of BLG was observed under the same experimental conditions. A similar pattern that a decrease in antigen binding potentials by OVO and an increase in antigen binding potentials by BLG A and B variants was noticed during dry heat treatment at temperatures 232C and above. Structural analyses were performed using circular dichroism spectroscopy (CD) and differential scanning calorimetry (DSC). Both proteins showed variations in the secondary structure when subjected to heating in water and PBS. In the presence of water, variable temperature scan with CD resulted in transition temperatures of OVO and BLG variants in the range of 70-75oC and 80-85oC respectively. There is no significant change in the secondary structure of BLG variants prepared in PBS. DSC study showed the transition temperatures of 84oC, 129oC for OVO and at 80oC, 195oC for BLG (A & B) variants under moist and dry heat conditions respectively. Overall, both proteins were highly resistant to thermal denaturation and retained their antigenic potential at typical cooking temperatures.
M.S. in Food Safety and Technology, May 2011
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- Title
- EFFICIENT SCORING AND RANKING OF EXPLANATION FOR DATA EXCHANGE ERRORS IN VAGABOND
- Creator
- Wang, Zhen
- Date
- 2014, 2014-05
- Description
-
Data exchange has been widely used in big data era. One challenge for data exchange is to identify the true cause of data errors during the...
Show moreData exchange has been widely used in big data era. One challenge for data exchange is to identify the true cause of data errors during the schema translation. The huge amount of data and schemas make it nearly impossible to find “the” correct solution. Vagabond system is developed to address this problem and use best-effort methods to rank data exchange error explanations base on the likelihood that they are the correct solutions. Ranking done on scoring functions that model some aspects of explanation sets. Examples of these properties include complexity(size of explana- tion), and side effect size(number of correct data values that will be affected by the changes). The thesis introduced three new scoring functions to increase the applicability of Vagabond under various data exchange scenarios. We prove that the monotonicity property required by Vagabond may not hold for some of the new scoring functions, so a new generic ranker is also introduced to efficiently rank error explanations for these new scoring functions as well as for future scoring functions that have boundary property. We can efficiently compute upper or lower bounds on the score of partial solutions. We also completed some performance experiments on the new scoring functions and the new ranker. The experiment result proves that the new scoring functions introduced in this thesis have a scalable performance.
M.S. in Computer Science, May 2014
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- Title
- Cure for the IKIA Syndrome : presented at IACRL 2008 conference: List of failures
- Creator
- Uth, Charles, Link, Jeanne
- Date
- 2008-02
- Description
-
Informal observations of a practical and creative approach piloting Blended Library Instruction for undergraduate Civil Architecture and...
Show moreInformal observations of a practical and creative approach piloting Blended Library Instruction for undergraduate Civil Architecture and Engineering students, in collaboration with faculty. At Illinois Institute of Technology students don’t receive library instruction as a required class or in tandem with a composition class. Faculty will schedule one-time sessions, which ideally should be planned with a class assignment in mind, but students are rarely engaged with a one time instruction. Many have IKIA syndrome or I Know It Already syndrome. The Millennials are a group that has integrated technology into every aspect of their lives and they assume that retrieving useful or necessary information will be easy. When they discover this isn’t the case lack of time, heightened anxiety, and increased frustration can prevent them from doing their best work. By intentionally creating a similar crisis prior to library instruction, students were more interested in what they stood to gain during pending library instruction. In this presentation we will discuss: 1) A creative means of delivering library instruction to a traditionally challenging population: engineering undergraduate students 2) Qualitative information collected via multiple assignments and interpreted in a quantitative fashion, as well as our observations. 3) A method for preparing students for library instruction that can be applied in almost any discipline without asking the instructor to sacrifice class time.
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- Title
- Optimal Behavior Modeling and Analysis of Electricity Market Participants
- Creator
- Li, Jie
- Date
- 2012-04-27, 2012-05
- Description
-
n restructured electricity power markets, competition among market participants is a key issue of concern for both the ISO (Independent System...
Show moren restructured electricity power markets, competition among market participants is a key issue of concern for both the ISO (Independent System Operator) and the market participants themselves. This dissertation analyzes the market behavior of both the generation side and demand side participants, and provides solution guidelines for devising effective competition strategies for market players’ profit maximization objectives. Generation side is the most competitive part in the electricity market with the unbundling of generation, transmission and distribution. Acting as self-interested entities, GENCOs (Generation Companies) are seeking effective and computationally efficient methodology for generation resource scheduling, while keeping its financial risks at acceptable levels when constituting bidding strategies. To help GENCOs achieve such goal, this dissertation propose a game theory based supply function like bidding model to construct the optimal bidding strategies for GENCOs in both energy and ancillary service markets. On the demand side, demand participation in the electricity market has already been advocated for a long time for its benefit to the entire market and the society as a whole. This dissertation focuses on a specific large electricity consumer type – Internet Data Center (IDC). By analyzing the unique energy consumption pattern for different IDC applications, this dissertation devises effective electric demand management solution for IDCs to conserve electricity energy consumption and cut electric bill, and quantifies the demand response effect of IDC on the electricity market.
Ph.D. in Electrical Engineering, May 2012
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- Title
- Fab Lab: Creating Design-to-Prototype Learning Modules at the Museum of Science and Industry (sequence unknown), IPRO 333 - Deliverables
- Creator
- Bonesz, Andrew, Clark, Howard, Douglas, Carlie, Gajdorus, Michael, Gottschall, Keenan, Hendricks, Rachel, Kimball, Clayton, Linares, Jared, Marks, Paul, Mellom, James, Oblenida, Cindy, Pop, Sabina, Stelcel, Carl, Young, Jeremy, Zhou, Raymond
- Date
- 2009-12
- Description
-
The primary objective of IPRO 333 is to partner the knowledge and ideas of young engineers, architects, and scientists at IIT with the...
Show moreThe primary objective of IPRO 333 is to partner the knowledge and ideas of young engineers, architects, and scientists at IIT with the resources of the Museum of Science and Industry (MSI) in Chicago. This partnership endeavors to help the museum's Fabrication Laboratory (Fab Lab) maximize its potential as a resource for museum guests, young and old, as well as for IIT students, staff, and faculty.
Sponsorship: Museum of Science and Industry. Steven Willis- Director, Fabrication Lab
Deliverables for IPRO 333: Fab Lab: Creating Design-to-Prototype Learning Modules at the Museum of Science and Industry for the fall 2009 semester
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- Title
- Tests on a Martin rotatory converter
- Creator
- Bacon, M. F., Rensch, R. H.
- Date
- 2009, 1919
- Publisher
- Armour Institute of Technology
- Description
-
http://www.archive.org/details/testsonmartinrot00baco
Thesis (B.S.)--Armour Institute of Technology; Bibliography: leaves i-ii
- Title
- Statistical monitoring of multivariable dynamic processes with state-space models
- Creator
- Negiz, A., Cinar, A.
- Date
- 1997-08
- Publisher
- AMER INST CHEMICAL ENGINEERS
- Description
-
Industrial continuous processes may have a large number of process variables and are usually operated for extended periods at fixed operating...
Show moreIndustrial continuous processes may have a large number of process variables and are usually operated for extended periods at fixed operating points under closed-loop control, yielding process measurements that are autocorrelated, cross-correlated and collinear. A statistical process monitoring (SPM) method based on multivariate statistics and system theory is introduced to monitor the variability of such processes. The statistical model that describes the in-control variability is based on a canonical-variate (CV) stare-space model that is an equivalent representation of a vector autoregressive moving-average rime-series model. The CV state variables obtained from the state-space model are linear combinations of the past process measurements that explain the variability of the future measurements the most. Because of this distinctive feature, the CV state variables are regarded as the principal dynamic directions A T-2 statistic based on the CV state variables is used for developing an SPM procedure. Simple examples based on simulated data and an experimental application based on a high-temperature short-time milk pasteurization process illustrate advantages of the proposed SPM method.
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- Title
- Particle production sources in heavy ion collisions at RHIC and LHC, Proceedings of the XLIII International Symposium on Multiparticle Dynamics
- Creator
- Wolschin, Georg
- Date
- 2013-09-15, 2013-09-15
- Publisher
- IIT Press
- Description
-
A nonequilibrium statistical relativistic diffusion model (RDM) with three sources is applied to the analysis of charged-hadron distributions...
Show moreA nonequilibrium statistical relativistic diffusion model (RDM) with three sources is applied to the analysis of charged-hadron distributions in Au–Au collisions at RHIC energies, in Pb–Pb collisions at the current LHC energy of 2.76 TeV, and in p–Pb at 5.02 TeV. The relative sizes of the particle production sources at RHIC and LHC energies are investigated in pseudorapidity space as functions of incident energy. The midrapidity source that arises mostly from gluon-gluon collisions becomes more important than the fragmentation sources as the energy increases from RHIC to LHC.
Sponsorship: IIT College of Science, High Energy Physics Division of Argonne National Laboratory
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- Title
- TWO PROBLEMS ON CROSSING NUMBERS
- Creator
- Wang, Lujia
- Date
- 2013-05-01, 2013-05
- Description
-
The crossing number of a graph G, cr(G) is the minimum number of intersections among edges over all possible drawings on a plane. The pairwise...
Show moreThe crossing number of a graph G, cr(G) is the minimum number of intersections among edges over all possible drawings on a plane. The pairwise crossing number pcr(G) is the the minimum number of pairs of edges that cross at least once over drawings. In the rst part of this survey, we deal with the conjecture that pcr(G) = cr(G), and prove that this is true for 4-edge weighted maps on the annulus. Moreover, we develop methods for solving analogous n-edge problems including the classi cation of permutations on a circle. In the second part, we de ne the generalized crossing number cri(G) as the crossing number of a graph on the orientable surface of genus i. The crossing sequence is de ned as (cri(G))g(G) i=0 , where g(G) is the genus of the graph. This part aims at the conjecture that for each sequence of four numbers decreasing to 0, there is some graph with such numbers as its crossing sequence. We come up with a particular family of graphs which have concave crossing sequences of length 4, but partially prove it.
M.S. in Applied Mathematics, May 2013
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- Title
- Learning Company, Literacy Center, Johannesburg, South Africa: learning co. aisling gray
- Creator
- Gray, Aisling
- Date
- 2010-07-29
- Title
- LICENSE PLATE RECOGNITION SYSTEM USING K NEAREST NEIGHBOR ALGORITHM
- Creator
- Xia, Yong
- Date
- 2012-12-03, 2012-12
- Description
-
License Plate Recognition (LPR) is an image-processing technology, also known as Automatic Number Plate Recognition (ANPR). This technology is...
Show moreLicense Plate Recognition (LPR) is an image-processing technology, also known as Automatic Number Plate Recognition (ANPR). This technology is very popular in fighting crime, locating stolen car, identifying parking-ticket and so on. In LPR system, the image is taken of the front or rear of the car and its quality needs to be enhanced for further process. With this enhanced image, first license plate region is located and extracted. Then character segmentation is performed on extracted license plate image. In this thesis, we use K Nearest Neighbor (KNN) algorithm to recognize these segmented characters. Keywords: LPR, Plate location, character segmentation, Image Processing, KNN
M.S.in Electrical Engineering, December 2012
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- Title
- THERMAL PROCESSING TO MITIGATE ARSENIC CONTENT IN NORTH AMERICAN RICE: TOTAL, SPECIATED ARSENIC AND NUTRIENT EVALUATION
- Creator
- Zhao, Pengyi
- Date
- 2015, 2015-05
- Description
-
Arsenic in the food supply has been a concern since public news reports in 2011 of the detection of arsenic in apple juice. Food and Drug...
Show moreArsenic in the food supply has been a concern since public news reports in 2011 of the detection of arsenic in apple juice. Food and Drug Administration (FDA) work on this issue has proposed a guidance for no more than 10 ppb of inorganic arsenic in apple juice. More recently rice harvested from the southern states of the United States is of concern of the arsenic content. Arsenic levels in rice have been attributed to the natural levels of arsenic in the soil and the farming practices used to grow rice. FDA released data that showed inorganic arsenic amounts in long grain white rice between 70 and 150 ppb. This work presents a process through washing/ rinsing to reduce the arsenic levels in prepared/cooked rice. Four different rice materials were obtained from Mississippi, Arkansas, Texas and Louisiana. Different processing methods such as common cooking, washing and cooking, excess water cooking, were used to prepare the rice. The common cooking method cooked the rice in a 2:1 (water : rice) ratio. The washing and cooking method rinsed a batch of rice with a 2:1 (water : rice) ratio at first, and then poured off wash water and added new water to cook rice in a 2:1 (water : rice) ratio. The excess water cooking method cooked the rice in excess water of a ratio of 4:1 (water : rice) and the excess water was removed after cooking. Controls of raw rice samples were also evaluated. The common cooked rice showed variable to no difference (-13.9% to 14.9%) from the raw control in arsenic retention. The washed and cooked rice showed a 9.8% to 36.8% reduction of arsenic from the control. The excess water cooked rice showed the greatest reduction of arsenic from 39.1% to 65.5% compared to the control. The species of arsenic mimic the total arsenic loss. There is a visible trend for reduction of arsenic content by washing, but the most reduction was achieved by cooking rice with an excess volume of water.
M.S. in Food Safety and Technology, May 2015
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- Title
- Development and Application of an Occupational Odor Hazard Index
- Creator
- Wang, Tingting
- Date
- 2011-04-24, 2011-05
- Description
-
Odors emitted from wastewater treatment and sludge processing facilities may lead to employee complaints regarding discomfort, stress or...
Show moreOdors emitted from wastewater treatment and sludge processing facilities may lead to employee complaints regarding discomfort, stress or disease, and affect productivity and worker turnover in Water Reclamation Plants (WRPs). This study reports and assesses a comprehensive method that estimates the odor perception and associated hazards from exposures to odors in a post-digestion dewatering building in a WRP and its vicinity areas. An Odor Reference Concentration (ORfC) is developed as an index of acceptable odor level. This index is applied to ensure that the majority of building occupants (80 percent or more) do not perceive the odor. This index is developed to fill the lack of a uniform standard and method to assess hazard of exposed individuals to odors in occupational environments and to regulate odor exposures.A comprehensive odor and odorant concentration database was formulated by a monitoring study in the occupational environment of a post-digestion dewatering building. The presence of odorants in the building are at concentrations below occupational exposure limits but higher than odor detection threshold values. This finding indicates that reducing odorant concentrations below exposure limits does not assure an odor-free environment. A model is formulated and validated for this dewatering building associating odor perception with concentrations of total sulfur compounds and relative humidity and is used for prediction of indoor odor concentrations under various conditions. Odor and odorant emission rates as the strength of sources are input variables of the indoor air quality model. In this study, odor and odorant emission rates from freshly dewatered biosolids in a dewatering building were measured using two widely used dynamic methods: the USEPA flux chamber and wind tunnel, and results from the two methods are not significantly different. Comparison of the two methods indicates that both methods can be used to estimate odor and odorant emission rates but the most effective and efficient method depends on prevailing environmental conditions. The ORfC established based on the comprehensive odor and odorant concentration database for this dewatering building is 13D/T (dilution to threshold). This index is used to evaluate seven control strategies recommended to reduce odor levels. If indoor odor concentrations in the occupational environment exceed the ORfC, then the hazard of odor exposures is unacceptable. Deterministic results of this study indicate that if appropriate control strategy is applied, odor concentration in the dewatering building would reach to below levels that cause unnecessary stress and other effects. The control strategy focus of this work is reduction of the indoor odor perception. But indoor control strategies must not cause outdoor odor problems to surrounding residential areas. Therefore, the potential impact of the control strategy recommended is also investigated in this thesis using the US EPA recommended air dispersion modeling AERMOD. Predictions of hydrogen sulfide concentrations at surrounding areas of the plant indicate that only one strategy, which proposes to add a new exhaust system in the dewatering building, would cause the ambient hydrogen sulfide concentration to be 7% higher than the odor detection threshold; other six strategies would not induce odor annoyance to surrounding areas. Acute and long-term ambient hydrogen sulfide exposure limits based on human health and irritation effects would not be violated under any of the seven control strategies.
Ph.D. in Environmental Engineering, May 2011
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- Title
- The titration of iron by potassium permanganate
- Creator
- Finkelstein, Leo
- Date
- 2009, 1914
- Publisher
- Armour Institute of Technology
- Description
-
http://www.archive.org/details/titrationofironb00fink
Thesis (B.S.)--Armour Institute of Technology
- Title
- Church & School Energy Efficiency and Financing Program (sequence unknown), IPRO 328 - Deliverables: IPRO 328 Final Report F09_redacted
- Creator
- Ciuffini, Kathryn, Kim, Ja Young, Knapczyk, Robert, Mckinley, Matthew, O'brien, Patrick, Maddamma, Todd, Schafer, Michael, Soderling, Philip, Wedster, Bonnie
- Date
- 2009-12
- Description
-
The Fall 2009 IPRO 328 team envisions the development and ultimately execution of a volunteer program which would facilitate the...
Show moreThe Fall 2009 IPRO 328 team envisions the development and ultimately execution of a volunteer program which would facilitate the implementation of energy saving improvements in a church and/or parochial school within the surrounding neighborhoods of IIT campus.
Sponsorship: Vince Cushing of Clean Urban Energy
Deliverables for IPRO 328: Church & School Energy Efficiency and Financing Program for the fall 2009 semester
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- Title
- APPROACHES TO QUANTIFY AND COMPARE THE THERMAL STABILITY OF FOOD ALLERGENS
- Creator
- Meng Xu
- Date
- 2013-04-24, 2013-05
- Description
-
Stability to heat or other food processing conditions has been suggested as one of the characteristics of food allergens, however there is in...
Show moreStability to heat or other food processing conditions has been suggested as one of the characteristics of food allergens, however there is in general a lack of standardized approach to determine or compare the thermal stabilities of food allergens. This study evaluated the use of several analytical tools including the BCA total protein assay, Far-UV Circular Dichroism Spectroscopy, Differential Scanning Calorimetry, and inhibition ELISA assays to study the changes in the structural and immunological properties of major allergens as a result of heat treatments, and identified parameters that can be used to quantify and compare the thermal stability of food allergens. Purified allergens from milk, egg, and almond were subjected to moist-heat or dry-heat treatments and changes in protein solubility, IC50 values and thermodynamic properties of each protein were determined. It was found that high transition temperature (Tm) was closely related to a greater resistance to changes in immunological properties after heat treatments, suggesting that it can be a good parameter to quantify and compare the thermal stability of different food allergens.
M.S. in Food Safety and Technology, May 2013
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- Title
- Cessation of Screech in Underexpanded Jets
- Creator
- Raman, G.
- Date
- 1997-04-10
- Publisher
- Cambridge Univ Press
- Description
-
In significantly underexpanded jets, screech inherently ceases to exist. This paper studies screech cessation in a supersonic rectangular jet...
Show moreIn significantly underexpanded jets, screech inherently ceases to exist. This paper studies screech cessation in a supersonic rectangular jet and provides an explanation for its occurrence. Experimental data are presented for fully expanded Mach numbers, M-j, ranging from 1.1 to 1.9. Screech becomes unsteady beyond M-j = 1.65 and ceases to exist beyond M-j = 1.75. The reason for this cessation has remained a mystery, and this paper examines three suspects: (i) the theory of a frequency mismatch between screech tones and the band of the most-amplified jet instability waves, (ii) the notion that Mach disk formation disrupts the shock-cell structure and weakens the screech-producing shocks, and (iii) the idea that acoustic feedback and receptivity diminish at high levels of underexpansion. A thorough interrogation of experimental data shows that (i) is not the main cause of screech cessation here, (ii) plays an insignificant role, and (iii) appears to have been largely responsible for screech cessation. Cessation occurs because feedback to the jet lip is diminished due to excessive expansion of the jet boundary. Further, since the jet lip now reflects and scatters low intensity sound, the end result is poor receptivity at the initial shear layer. This theory is substantiated by the re-activation of screech when the nozzle lip thickness is made larger than the expanded jet boundary. Finally, increasing lip thickness is seen to produce a systematic shift (to higher M-j) of the onset of cessation. The results of this study are of direct relevance to the sonic fatigue problem in aircraft structures, because understanding screech helps prevent such damage.
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