Tesi sul tema "Freezing"
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1
Zhang, Qi. "Freezing tolerance in zoysiagrass". Diss., Manhattan, Kan. : Kansas State University, 2007. http://hdl.handle.net/2097/448.
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2
Pande, Vijay Satyanand. "Freezing transition of heteropolymers". Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/33262.
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3
Ahmad, Mansour M. M. "Assessment of freezing desalination technologies". Thesis, Swansea University, 2012. https://cronfa.swan.ac.uk/Record/cronfa42635.
Testo completoAbstract (sommario):
The production of both fresh water and waste streams are progressively increasing over the years due to ongoing population growth coupled with high levels of increase in water consumption. The ongoing growth of human activities, such as industry, recreation, and agriculture, are significantly contributing to the increase in both water demand and severity of degradation of natural water resources. The majority of the industrial wastewaters have a significant impact on the environment; some of which may pose a number of threats to human health and the surrounding environment. Thus, discharge of such waste streams into a surface water and/or groundwater presents a major source of water pollution in many countries. Therefore, these waste streams must be disposed of in an environmentally acceptable manner. The primary concern of the PhD thesis is to seek the most feasible and applicable freezing desalination technologies that are potentially capable to concentrate the dissolved ionic content of the liquid streams, especially for those causing severe pollution problems. Therefore, various forms of melt crystallisation processes, namely; agitated and static crystallisation processes, ice maker machines, a Sulzer falling film crystallisation process, the Sulzer suspension crystallisation process, and the Sulzer static crystallisation process, were experimentally used and investigated. The experimental investigations were carried out on the laboratory bench scale and/or straightforward pilot plant by using aqueous solutions of sodium chloride and/or process brines as feed samples. The study was focused on a number of important parameters influencing the separation performance of the investigated treatment systems. In general, the resulting experimental data for each innovative process were highly encouraging in minimising the volume of the waste stream, and substantially increasing the amount of product water. The obtained product water was ready for immediate use either as drinking water or as a saline water of near brackish water or seawater qualities. Also, relationships between the influences and the separation performance, in terms of salt rejection and water recovery ratios, were explored and determined for the investigated technologies. Based on the experimental results, the Sulzer melt crystallisation processes were scaled up and were combined into a commercial reverse osmosis membrane desalination plant. As a result, three novel treatment option configurations were proposed for minimising the waste stream, whilst increasing the production rate of drinking water and/or preserving a substantial amount of natural water resource from the RO plant's exploitation.
4
Wood, John Anderson Carleton University Dissertation Geology. "Internal pressures in freezing soils". Ottawa, 1985.
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5
Griffin, Joshua E. "Wastewater Irrigation in Freezing Conditions and the Impacts to Runoff Water Quality and Soil Freezing". The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1420584627.
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6
Han, Sangjoon. "Modeling the mechanics of freezing clay". College Park, Md. : University of Maryland, 2005. http://hdl.handle.net/1903/3441.
Testo completoAbstract (sommario):
Thesis (Ph. D.) -- University of Maryland, College Park, 2005.Thesis research directed by: Civil Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
7
Beerman, Michael. "Transverse freezing of thin liquid films /". Thesis, Connect to this title online; UW restricted, 2007. http://hdl.handle.net/1773/10573.
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8
Karlsson, Ami. "Purifying contaminated water by eutectic freezing". Thesis, Umeå universitet, Kemiska institutionen, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-85836.
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9
Noon, C. "Secondary frost heave in freezing soils". Thesis, University of Oxford, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.360418.
Testo completoAbstract (sommario):
Frost heave describes the phenomenon whereby soil freezing causes upwards surface motion due to the action of capillary suction imbibing water from the unfrozen region below. The expansion of water on freezing is a small part of the overall surface heave and it is the flow of water towards the freezing front which is largely responsible for the uplift. In this thesis, we analyse a model of frost heave due to Miller (1972, 1978) which is referred to as `secondary frost heave'. Secondary frost heave is characterised by the existence of a `partially frozen zone', underlying the frozen soil, in which ice and water coexist in the pore space. In the first part of the thesis we follow earlier work of Fowler, Krantz and Noon where we show that the Miller model for incompressible soils can be dramatically simplified. The second part of the thesis then uses this simplification procedure to develop simplified models for saline and compressible soils. In the latter case, the development of the theory leads to the consideration of non-equilibrium soil consolidation theory and the formation of segregated massive ice within permafrost. The final part of the thesis extends the simplified Miller model to the analysis of differential frost heave and the formation of patterned ground (e.g. earth hummocks and stone circles). We show that an instability mechanism exists which provides a plausible theory for the formation of these types of patterned ground.
10
Knutsson, Sven. "Soil behavior at freezing and thawing". Doctoral thesis, Luleå tekniska universitet, Geoteknologi, 1998. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-25923.
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Avhandlingens första del behandlar en teoretisk beräkningsmodell för tjällyftning samt studier av dess noggranhet i olika situationer. Tjällossningsförloppet analyseras och studeras genom noggranna mätningar av porvattentryckens fördelning i tid och rum. Porvattentrycksutvecklingen kopplas till läget av islinserna i jorden, som detekteras med hjälp av röntgenteknik. Avhandlingens andra del belyser hur frusen jord kan packas och vad deformationerna i sådan jord blir då den tinar. Beräkningar av kompressionen i samband med upptining jämförs med resultat från såväl laboratorieförsök som uppföljningar i fält. Strukturella förändringar i jorden till följd av frysning och tining belyses också.Godkänd; 1998; 20061123 (haneit)
11
Dickens, Dustin. "Supercooling and Freezing of HNO3/H2O Aerosols". Thesis, University of Waterloo, 2000. http://hdl.handle.net/10012/1225.
Testo completoAbstract (sommario):
The freezing kinetics of binary nitric acid/water aerosols is of fundamental importance to the modelling of polar stratospheric clouds and the role they in ozone depletion over the Arctic/Antarctic regions. Cirrus clouds are also often composed of nitric acid solutions, hence an understanding of freezing process in these aerosols also aids in modelling the earth's radiation budget and global warming. This thesis explores the kinetic phase diagram of nitric acid/water aerosols with sizes ranging between 0. 2 and 1. 5 mm in radius and concentrations ranging between pure water and 0. 45 mole fraction HNO3. Although the kinetic phase diagram has now been studied between 0. 46 mole fraction HNO3 and pure water, more data is needed in the region between 0. 18 and 0. 25 mole fraction HNO3 to confirm the results reported.
The project described in this thesis are a continuation of a project begun by Allan Bertram. The measurements involving aerosols with compositions greater than 0. 25 mole fraction HNO3 were carried out as part of Allan Bertram's Ph. D. thesis (see ref. 20) These data were later examined using a more comprehensive data analysis method (as presented in this thesis) in an effort to obtain a more complete understanding of this system.
12
Stephenson, Neil. "On-farm blast freezing of Saskatoon berries". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/MQ57583.pdf.
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13
Cornell, Stephen John. "Studies of freezing in kinetic Ising models". Thesis, University of Oxford, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.257825.
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14
Ash, Philip Andrew. "Surface freezing in surfactant/alkane/water systems". Thesis, Durham University, 2011. http://etheses.dur.ac.uk/843/.
Testo completoAbstract (sommario):
Surface freezing transitions in mixed monolayers of a homologous series of cationic surfactants, the alkyltrimethyl ammonium bromides (CnTAB where n = 12, 14, 16, 18), as well as a range of non-ionic, zwitterionic and biological surfactants, have been investigated ellipsometrically with a range of n-alkanes (Cm where m = 12 – 20, 28). Two distinct solid phases are observed depending upon the chain length difference between surfactant and n-alkane. Type I solid phases consist of a surface frozen mixed monolayer and are formed when this difference is small. Type II solid phases are bilayer structures with a frozen layer of neat n-alkane above a liquid-like mixed monolayer. Type II freezing was thought to occur via wetting of surface frozen n-alkane, as previously reported type II transitions took place in the presence of surface frozen n-alkanes. Thermodynamically stable type II solid phases have now been found in the presence of n-alkanes that do not show surface freezing at the air/alkane interface, however, and so this picture is incomplete. In the presence of pentadecane, for example, the biological surfactant lyso-OPC forms a stable type II solid phase 6.5 °C above the n-alkane bulk melting point. Such a large surface freezing range is unprecedented for a type II system. Studies using external reflection FTIR (ER-FTIRS) and vibrational sum-frequency spectroscopies (VSFS) have been used to probe these novel behaviours. Results were fully consistent with the proposed structures of both type I and type II surface frozen layers. 2D correlation analysis of ER-FTIR spectra as a function of temperature showed that type II frozen layer formation does not proceed via a simple wetting transition, with the formation of a transient intermediate implied. Evidence for such an intermediate was provided by dynamic ellipsometry measurements on the type II C18TAB/n-eicosane system.
15
Huang, Jen-Yi. "Fundamental features of food fat freezing fouling". Thesis, University of Cambridge, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.607795.
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Saranovic, Filip. "Private international law aspects of freezing injunctions". Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/270457.
Testo completoAbstract (sommario):
The Commercial Court in London is frequently dealing with applications for a freezing injunction. The vast majority of academic literature and court decisions directly or indirectly adopt the view that freezing injunctions have stood the test of time and are so frequently granted in commercial litigation that there is no need for any serious concern about their scope, let alone the need to identify and question the legitimacy of the justifications for their existence. Contrary to the traditional view, this thesis has identified equipage equality as the primary function of freezing injunctions. This recognition that freezing injunctions seek to establish a level-playing field in litigation has led the author to conclude that the current scope of the relief is excessively claimant-friendly and involves illegitimate interference with the sovereignty of foreign states. Taking into account the tactical reasons for seeking a freezing injunction, the author challenges the current interpretation of the substantive preconditions for granting the relief. Their current interpretation does not strike a fair balance between the interests of the parties. The author argues that these concerns are exacerbated by the current international scope of freezing injunctions due to the insufficient regard for the principles of public international law. The encroachment on the jurisdiction of foreign states undermines equipage equality by enabling claimants to make multiple applications for interim relief in respect of the same assets. In the light of the above, the author has sought to make a range of proposals to restrict the scope of freezing injunctions with the aim of bringing the relief in line with equipage equality.
17
Dickens, Dustin. "Supercooling and freezing of HNO₃/H₂O aerosols". Waterloo : University of Waterloo, [Dept. of Chemistry], 2000. http://etd.uwaterloo.ca/etd/ddickens2000.pdf.
Testo completoAbstract (sommario):
Thesis (M.Sc)-University of Waterloo, 2000."A thesis presented to the University of Waterloo in fulfilment of the thesis requirement for the degree of Master of Science in Chemistry". Includes bibliographical references.
18
Tommik, Karina. "Consolidation of Soft Sediments Using Artificial Ground Freezing". Thesis, Luleå tekniska universitet, Geoteknologi, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-66574.
Testo completoAbstract (sommario):
Freeze-thaw cycling is investigated as a possible method for consolidation of fine grained soils. The method relies mainly on phenomena of thaw consolidation. While the soil is subjected to multiple freeze-thaw cycles the water is pressed out of the material as the excess pore pressure dissipates. To prove that this phenomenon can be used to consolidate fine grained soils several laboratory tests are conducted. Oedometer test are conducted with alternating freeze-thaw cycles at different load. Unconfined soil specimens are also frozen to assess the effect of freeze-thaw cycling on plastic and liquid limit and also to determine how much free water is produced in the process. A larger scale test is conducted to provide a better understanding about how the method could work in reality. It is proven that it is possible to significantly lower the water content of the tested material by using freeze-thaw cycles. It is concluded that liquid and plastic limits as well as the void ratio of the material decrease with increasing number of freeze-thaw cycles.
19
Andersson, Martin, e Marcus Olofsson. "Methods for Freezing Time with Computer Graphics Imagery". Thesis, Högskolan i Gävle, Avdelningen för Industriell utveckling, IT och Samhällsbyggnad, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:hig:diva-8666.
Testo completoAbstract (sommario):
The most effective method to create an illusion of frozen time in film media was explored for this research. Starting with a description and evaluation of different methods of achieving the effect, this document describes the implementation of a specific technique for a particular project to test freezing time. It was also established to aid students in their understanding of the process in both pre- and post-production. After testing and researching, the method of filming still-posing actors with a high speed camera was chosen. However, the testing and pre-production phase demanded a large amount of time, therefore for the remainder of the project only one scene was established. For budget and time consuming purposes the two recommended techniques are; camera projection and filming still-posing actors with a high speed camera. The choice between these two methods mainly depends on the amount of camera movement.
20
Erfani, Majid-Reza. "De-aggregated reliability analysis of freezing rain hazard". Thesis, McGill University, 2010. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=86822.
Testo completoAbstract (sommario):
This work addresses issues for improving the estimation of the recurrence rate and the distribution in severity of extreme ice events in the Montreal area, which is required in order to determine design criteria for structures such as electric transmission lines. Some of the limitations of current methods for studying extreme freezing rain events are due to the relatively short data records. This results in variability of 'at site' data sets that have only a few large accumulations. The methods developed in this work address these issues. First, de-aggregated analysis is used to obtain better statistical fits by grouping storms according to physical variables that are correlated with the occurrence of ice storms (spatial patterns of sea level pressure (SLP) or 1000 to 500 hPa geopotential height anomalies). And second a procedure to decrease the uncertainty on estimates of the hazard function at high return periods based on solving the CRREL Simple icing model using reliability method is developed. In this procedure, uncertainty is propagated through the model by treating it as a function of random variables.Anomaly maps of several meteorological variables were investigated for the objective categorization of ice storms. The NCEP reanalysis data was used to compile spatial patterns for the analysis of the storms identified and categorized by Rauber et al (2001). Several multivariate statistical analysis procedures were used to investigate the effectiveness of sea level pressure, the 1000 to 500 hPa, and the 1000 to 925 hPa geopotential heights for clustering these storms. Results indicated that the k-means algorithm applied to principle component scores of the storm anomaly maps provided the best clustering results. The results indicated that storms with higher precipitations belong to a group associated with the phenomena of cold air damming as a result of the Appalachian Mountains.
Environment Canada hourly data was used to identify freezing rain events and obtain measurements of wind speed and precipitation during the events that occurred over Ottawa, Montreal, and Quebec City. General Pareto or Generalized Extreme Value distributions are fitted to the data of total precipitation or total radial ice accumulation for each cluster using a peaks-over-threshold approach. Statistical tests indicate the resulting distributions for precipitation are significantly different from each cluster. This de-aggregated approach improves estimates of the icing hazard by improving statistical fits and by reducing the sensitivity of the results to the choice of threshold.
The second approach used to improve the estimates of the icing hazard function, using reliability methods, considers total precipitation, freezing ratio, and wind speed as the random variables in solving the icing model. The most likely combination of variables associated with high ice accumulations was found to high total precipitation, high freezing ratios, but only slightly higher than average wind speed. The latter is useful for defining load combinations (wind speed and ice accumulation) for structural design purposes.
Finally, the superstation approach of Jones and White (2002a) was investigated by combining Environment Canada data for Ottawa, Montreal and Quebec City. Monte Carlo simulations were performed on the regional set of data using 'at site' indexes. The reliability analysis of empirical icing equation produced results similar to Jones and White at quantiles associated with the 50 year return period. However there were greater differences at higher quantiles. The estimated return periods for radial ice accumulations of 45mm are 160, 210, and 85 years for Montreal, Ottawa, and Quebec City respectively.
L'objectif de ce travail est d'améliorer l'estimation du taux de récurrence et la distribution de la sévérité des tempêtes de verglas dans la région de Montréal ; deux quantités requises pour déterminer les critères de conception de certaines structures, telles que les lignes de transmission, pour ce type d'événement. Certaines des faiblesses des méthodes actuelles pour étudier les événements de pluies verglaçantes sont liées à la disponibilité limitée de données. Cela se traduit par des observations variables et un faible nombre d'événements importants. Les méthodes développées dans ce travail adressent ces problèmes. En premier lieu, une analyse désagrégée est employée afin d'obtenir de meilleures tendances statistiques en regroupant les tempêtes en fonction de différentes caractéristiques physiques qui sont reliées aux événements de verglas. Une deuxième procédure pour diminuer l'incertitude reliée à l'estimation de la période de récurrence des événements extrêmes est basée sur la solution du modèle d'accumulation CRREL à l'aide de méthodes d'analyse fiabilistes.
Les données de réanalyse du NCEP ont été utilisées pour compiler les relations spatiales entre les paramètres météorologiques pour les tempêtes identifiées et classifiées par Rauber et al. (2001). Plusieurs analyses statistiques à variables multiples ont été utilisées afin d'évaluer l'efficacité de le pression au niveau de la mer, de l'épaisseur de la couche atmosphérique entre 1000 et 500 hPa et de l'épaisseur de la couche atmosphérique entre 1000 et 925 hPa à regrouper les tempêtes. Les résultats indiquent que l'algorithme k-means couplé avec une représentation par composantes principales des tempêtes produit les meilleurs résultats. Les tempêtes avec des précipitations plus élevées sont associées à un groupe où les systèmes de haute pression sont ralentis ou stoppés momentanément par les Appalaches.
Les observations d'environnement Canada ont été utilisées pour identifier les tempêtes de verglas qui ont affecté Ottawa, Montréal et Québec et obtenir un échantillon de la vitesse des vents et des précipitations. Les précipitations totales et l'accumulation de verglas pour chaque groupe sont représentées par les distributions General Pareto et Generalized Extreme Value, en combinaison avec une approche Peaks over Treshold. Les distributions obtenues diffèrent de façon importante pour les différents regroupements. L'approche par désagrégation améliore la performance des modèles et est moins sensible au choix des précipitations minimales (le treshold).
La seconde approche pour l'estimation de la période de retour des événements de verglas extrêmes considère la précipitation totale, la proportion du gel et la vitesse du vent comme des variables aléatoires dans le modèle d'accumulation de verglas. La combinaison la plus probable des variables associée à des accumulations de verglas importantes correspond à une précipitation totale et une proportion de gel élevées, mais une vitesse du vent seulement légèrement plus haute que la moyenne. Cette information est utile à l'identification des cas de combinaison des charges (vitesse de vent et accumulation de verglas) pour les critères de conception.
Finalement, la méthode des super-stations (Jones and white 2002a) a été analysée pour un échantillon regroupant les villes d'Ottawa, Québec et Montréal. Des simulations Monte Carlo ont été effectuées sur les données régionales et cette approche fiabiliste, appliquée au modèle empirique d'accumulation, donne des résultats similaires à ceux de Jones et White (2002a) pour une période de retour de 50 ans, mais les divergences sont plus importantes pour des périodes de retour plus élevées. Les périodes de retour correspondant à une accumulation de verglas de 45mm pour Montréal, Ottawa et Québec sont de 160, 210 et 85 ans, respectivement.
21
Yuh, Seon Hee. "Cloning genes differentially expressed in freezing tolerant orchids". Virtual Press, 1996. http://liblink.bsu.edu/uhtbin/catkey/1020165.
Testo completoAbstract (sommario):
Genes responsible for differences in gene regulation and expression in normal cells and freezing tolerant cells were identified using two related wintergreen orchid species, Aplectrum hyemale and Tipularia discolor. Changes in gene expression observed in field-collected tissues obtained from different seasons were compared as were changes observed in plants subjected to cold shock in a laboratory environmental chamber. In order to clone these differentially expressed genes which may confer photosynthesis cold tolerance, the recently developed technique, mRNA differential display was employed. Using this process, mRNA was isolated from the tissue and reverse transcribed to cDNAs, which were amplified using specific anchored 3' primers and various random 5' primers. The 50-100 bands resulting from specific primers were compared on denaturing polyacrylamide gels. Bands differently expressed were excised from the gel and purified. In the future, if partial sequence analysis indicates they may code important regulatory proteins, they will be used as probes to obtain full-length genes from a cDNA library for further characterization. This study provides an opportunity not only to obtain important regulatory genes in plants, but also to understand more about temperature regulated gene expression in orchids.Department of Biology
22
Hampton, Christopher N. "Strength and creep testing for artificial ground freezing". Thesis, University of Nottingham, 1986. http://eprints.nottingham.ac.uk/12176/.
Testo completoAbstract (sommario):
Artificial ground freezing (AGF) provides a means by which excavations can be given temporary or permanent structural support. It may also be used to control the movement of groundwater without the risk of pollution of potable aquifers. As AGF is called upon to strengthen ground at ever increasing depths, the design process needs to be adapted to account for the greater stresses encountered. In strong materials, the prime consideration is the short term strength of the materials and closed-form formulae can be used in design. In weaker materials, the time dependent creep behaviour of the frozen ground predominates and more complex analysis techniques have been devised (e. g. finite elements). Previous works in this field have been chiefly concerned with uniaxial states of stress. In this thesis, consideration is given to the problem of modelling creep under triaxial stress conditions. An introduction is followed by an outline of the general applications and design procedures currently used in ice wall design. Descriptions are then given of a selection of soils and weakly cemented rocks which have been incorporated into a programme of tests to investigate both short and long term strength behaviour. The apparatus available at the start of this project was suitable for uniaxial and low pressure triaxial tests only. Equipment subsequently developed to extend the confining pressure capability to 12 MPa, is described in detail. Short term strength tests show the increase in strength on freezing of ground materials is almost entirely due to the cohesion contributed by the ice matrix. Analysis of the creep test results leads to the development of a new empirically based triaxial creep equation for frozen soils. A sensitivity analysis of the parameters in this equation is followed by its application to a simplified design. Suggestions for further work in this field are included.
23
Wang, Rui. "Freezing and freeze-drying highly concentrated carbohydrate systems". Thesis, University of Birmingham, 2017. http://etheses.bham.ac.uk//id/eprint/7528/.
Testo completoAbstract (sommario):
Freeze drying is a widely-used dehydration technique in food and pharmaceutical industry, involves water crystallisation (freezing) and ice sublimation during the process. The purpose of the study is to enable the initial concentration of solutions that are used in freezing and freeze drying processes to be increased, as an approach to reduce the energy consumption of the process. Spontaneous crystallisation from both sucrose solutions and coffee solutions was studied by DSC, XRD and cryo-SEM, and results showed that increasing solid concentration (up to 70%) significantly delayed the water crystallisation, shown as lower crystallisation temperature and less or even no ice crystal formation. A method was developed to induce water crystallisation by adding already formed ice seeds to water, which allowed the study of ice crystal growth rate at controllable conditions. The method combined the use of a temperature controlled stage and an optical microscope, and the effects of solid concentration (up to 60%), temperature, viscosity, solute type, and air bubbles on crystal growth were investigated. Freeze drying high concentration sucrose (up to 60%) showed significant volume expansion (collapse), and methods to reduce the collapse were tried by modifying the formulation (adding high molecular weight gum Arabic) or freeze drying cycles (reducing heating rate between primary and secondary drying). Results showed that the up to 30% concentration of sucrose solution can be dried without volume expansion with modified freeze drying process.
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Saad, Ali. "Detection of Freezing of Gait in Parkinson's disease". Thesis, Le Havre, 2016. http://www.theses.fr/2016LEHA0029/document.
Testo completoAbstract (sommario):
Le risque de chute provoqué par le phénomène épisodique de ‘Freeze of Gait’ (FoG) est un symptôme commun de la maladie de Parkinson. Cette étude concerne la détection et le diagnostic des épisodes de FoG à l'aide d'un prototype multi-capteurs. La première contribution est l'introduction de nouveaux capteurs (télémètres et goniomètres) dans le dispositif de mesure pour la détection des épisodes de FoG. Nous montrons que l'information supplémentaire obtenue avec ces capteurs améliore les performances de la détection. La seconde contribution met œuvre un algorithme de détection basé sur des réseaux de neurones gaussiens. Les performance de cet algorithme sont discutées et comparées à l'état de l'art. La troisième contribution est développement d'une approche de modélisation probabiliste basée sur les réseaux bayésiens pour diagnostiquer le changement du comportement de marche des patients avant, pendant et après un épisode de FoG. La dernière contribution est l'utilisation de réseaux bayésiens arborescents pour construire un modèle global qui lie plusieurs symptômes de la maladie de Parkinson : les épisodes de FoG, la déformation de l'écriture et de la parole. Pour tester et valider cette étude, des données cliniques ont été obtenues pour des patients atteints de Parkinson. Les performances en détection, classification et diagnostic sont soigneusement étudiées et évaluéesFreezing of Gait (FoG) is an episodic phenomenon that is a common symptom of Parkinson's disease (PD). This research is headed toward implementing a detection, diagnosis and correction system that prevents FoG episodes using a multi-sensor device. This particular study aims to detect/diagnose FoG using different machine learning approaches. In this study we validate the choice of integrating multiple sensors to detect FoG with better performance. Our first level of contribution is introducing new types of sensors for the detection of FoG (telemeter and goniometer). An advantage in our work is that due to the inconsistency of FoG events, the extracted features from all sensors are combined using the Principal Component Analysis technique. The second level of contribution is implementing a new detection algorithm in the field of FoG detection, which is the Gaussian Neural Network algorithm. The third level of contribution is developing a probabilistic modeling approach based on Bayesian Belief Networks that is able to diagnosis the behavioral walking change of patients before, during and after a freezing event. Our final level of contribution is utilizing tree-structured Bayesian Networks to build a global model that links and diagnoses multiple Parkinson's disease symptoms such as FoG, handwriting, and speech. To achieve our goals, clinical data are acquired from patients diagnosed with PD. The acquired data are subjected to effective time and frequency feature extraction then introduced to the different detection/diagnosis approaches. The used detection methods are able to detect 100% of the present appearances of FoG episodes. The classification performances of our approaches are studied thoroughly and the accuracy of all methodologies is considered carefully and evaluated
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Waller, Deborah. "Environmental scanning electron microscopy of freezing aqueous solutions". Thesis, University of Cambridge, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.613409.
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Kondrashova, Daria, e Rustem Valiullin. "Diffusion in mesoporous materials during melting and freezing". Diffusion fundamentals 16 (2011) 51, S. 1, 2011. https://ul.qucosa.de/id/qucosa%3A13792.
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Combes, Pierre. "Freezing a la marche et syndromes extra-pyramidaux". Toulouse 3, 1994. http://www.theses.fr/1994TOU31071.
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Liu, Zhen. "Multiphysics Simulation and Innovative Characterization of Freezing Soils". Case Western Reserve University School of Graduate Studies / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=case1350331910.
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Guevara, Fernando Irons Gordon A. "A study of slag freezing in metallurgical furnaces". *McMaster only, 2007.
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30
Zhen, Ying. "Natural variation in freezing tolerance in Arabidopsis thaliana". Diss., Manhattan, Kan. : Kansas State University, 2009. http://hdl.handle.net/2097/2165.
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Claes, Dennis C. "Mixed layer dynamics in the onset of freezing". Thesis, Monterey, California : Naval Postgraduate School, 1990. http://handle.dtic.mil/100.2/ADA241787.
Testo completoAbstract (sommario):
Thesis (M.S. in Meteorology and Oceanography)--Naval Postgraduate School, December 1990.Thesis Advisor(s): Garwood, Roland W. Second Reader: Davidson, Kenneth L. "December 1990." Description based on title screen as viewed on April 02, 2010. DTIC Descriptor(s): Temperature, dynamics, layers, flux(rate), energy, rates, sensitivity, depth, surfaces, nonlinear systems, solutions(general), freezing, heating, wind velocity, mixing, mixed layer(marine), salinity, heat flux, surface temperature, wind stress, buoyancy, hyperbolas, models DTIC Identifier(s): Ocean models, mixed layer (marine), freezing, sea ice, sea water, air water interactions, temperature, salinity, wind forcing, layers, depth, turbulence, mixing, wind velocity, freezing rate, parametric analysis, theses. Author(s) subject terms: Oceanography, sea ice, mixed layer modeling, freezing Includes bibliographical references (p. 93-99). Also available in print.
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Atkinson, James David. "Freezing of droplets under mixed-phase cloud conditions". Thesis, University of Leeds, 2013. http://etheses.whiterose.ac.uk/5858/.
Testo completoAbstract (sommario):
Mixed-phase clouds contain both liquid and ice particles. They have important roles in weather and climate and such clouds are thought to be responsible for a large proportion of precipitation. Their lifetime and precipitation rates are sensitive to the concentration of ice. This project focuses upon the formation of ice within clouds containing liquid droplets colder than 273 K. A new bench-top instrument has been developed to study ice nucleation in liquid droplets. Pure water droplets of sizes relevant to clouds in the lower atmosphere do not freeze homogeneously until temperatures below ~237 K are reached. However, literature measurements of nucleation rates are scattered over two kelvin and there is uncertainty over the actual mechanism of ice formation in small droplets. The freezing of droplets with diameters equivalent to ~4 – 17 μm has been observed. It was found that ice nucleation rates in the smallest droplets of this size range were consistent with nucleation due to the droplet surface, but that surface nucleation does not occur at fast enough rates to be significant in the majority of tropospheric clouds. Water droplets can be frozen at higher temperatures than relevant for homogeneous freezing due to the presence of a class of aerosol particles called ice nuclei. Field observations of ice crystal residues have shown that mineral dust particles are an important group of ice nuclei, and the ice nucleating ability of seven of the most common minerals found in atmospheric dust has been described. In comparison to the other minerals, it was found that the mineral K-feldspar is much more efficient at nucleating ice. To relate this result to the atmosphere, a global chemical and aerosol transport modelling study was performed. This study concluded that dust containing feldspar emitted from desert regions reaches all locations around the globe. At temperatures below ~255 K, the modelled concentration of feldspar is sufficient to explain field observations of ice nuclei concentrations.
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Kondrashova, Daria, e Rustem Valiullin. "Diffusion in mesoporous materials during melting and freezing". Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-185365.
Testo completo
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Rogers, Maile Anne. "Water Vapor Movement in Freezing Aggregate Base Materials". BYU ScholarsArchive, 2013. https://scholarsarchive.byu.edu/etd/4013.
Testo completoAbstract (sommario):
The objectives of this research were to 1) measure the extent to which water vapor movement results in water accumulation in freezing base materials; 2) evaluate the effect of soil stabilization on water vapor movement in freezing base materials; 3) determine if the corresponding changes in water content are sufficient to cause frost heave during winter; 4) determine if the corresponding changes in water content are sufficient to cause reductions in stiffness during spring; 5) evaluate relationships between selected material properties, freezing conditions, and the occurrence and impact of water vapor movement; and 6) numerically simulate heat and water movement in selected pavement design scenarios. The research involved extensive laboratory and field testing, statistical analyses, and numerical modeling. The results of the laboratory testing, which included gradations, Atterberg limits, soil classifications, specific gravity and absorption values, electrical conductivity values, moisture-density relationships, soil-water characteristic curves, moisture-stiffness curves, hydraulic conductivity values, and frost susceptibility assessments, were used to characterize each material and enable subsequent statistical analyses. Testing of both treated and untreated materials enabled investigation of a wide variety of material properties. The results of the field testing, which included temperature, moisture content, water potential, elevation, and stiffness data over time, provided the basis for comparing pavement sections with and without capillary barriers and established the framework for numerical modeling. In a pavement section with a capillary barrier underlying the base layer, water vapor movement from the subgrade through the capillary barrier may be expected to increase the water content of the base layer by 1 to 3 percent during a typical winter season in northern Utah for base materials similar to those studied in this research. During winter, cold temperatures create an ideal environment for water vapor to travel upward from the warm subgrade soil below the frost line, through the capillary barrier, and into the base material. Soil stabilization can lead to increased or decreased amounts of water vapor movement in freezing base materials depending on the properties of the stabilized soil, which may be affected by gradation, mineralogy, and stabilizer type and concentration. Accumulation of water from long-term water vapor movement into frost-susceptible base materials underlain by a capillary barrier can lead to frost heave of the base layer as it approaches saturation, as water available in the layer can be redistributed upwards to create ice lenses upon freezing. However, the incremental increase in total water content that may occur exclusively from water vapor movement during a single winter season in northern Utah would not be expected to cause measurable increases in thaw weakening of the base layer during spring. Because water in a base layer overlying a capillary barrier cannot drain until nearly reaching positive pore pressures, the base layer will remain indefinitely saturated or nearly saturated as demonstrated in this research. For materials similar to those studied in this research, potentially important material properties related to the occurrence of water vapor movement during freezing include dry density, percent of material finer than the No. 200 sieve, percent of material finer than 0.02 mm, apparent specific gravity, absorption, initial water content, porosity, degree of saturation, hydraulic conductivity, and electrical conductivity. The rate at which water vapor movement occurs is also dependent on the thermal gradient within the given material, where higher thermal gradients are associated with higher amounts of water vapor movement. The numerical modeling supported the field observations that the capillary barrier effectively trapped moisture in the overlying base material, causing it to remain saturated or nearly saturated throughout the monitoring period. Only non-frost-susceptible aggregate base materials should be specified for use in cold climates in conjunction with capillary barriers, and the base material in this case should be assumed to remain in a saturated or nearly saturated condition during the entire service life of the pavement. Further study is recommended on water vapor movement in freezing aggregate base materials.
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Kröger, Jens 1981. "Elastic behavior and freezing of crystals with square symmetry". Thesis, McGill University, 2005. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=84048.
Testo completoAbstract (sommario):
The main purpose of this thesis is to justify the density functional theory of freezing in the case of a crystal with square symmetry. In the first part, I discuss the widely used technique of molecular dynamics to characterise the dynamics and statistical observables of a system undergoing a phase transition. I then outline the advantages and the main drawbacks of this technique: slow implementation and poor performance for long time scales. It is shown that order parameter or phenomenological theories of freezing paliate those problems. These theories describe the dynamics of one parameter that starts in a highly symmetric state and which symmetry is broken during the phase transition. The dynamics of the order parameter, which in our case is the time averaged density, is governed by the topology of a free energy functional. We derive such a free energy functional for two theories and explain why one of these can be applied to give freezing into arbitrary symmetry groups. The study of freezing into square symmetry and various elastic deformations of two-dimensional crystals form the last part of the thesis.
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Glendinning, Mark Charles. "Modelling the freezing and thawing behaviour of saturated soils". Thesis, Cardiff University, 2007. http://orca.cf.ac.uk/54607/.
Testo completoAbstract (sommario):
This thesis presents an investigation of the thermo / hydro / mechanical behaviour of saturated soils with cryogenic suction effects. The flow relationships accommodate a number of mechanisms: i) heat transfer by conduction, convection, and latent heat transfer and ii) moisture transfer in the liquid phase due to pressure head, elevation head, and thermal gradients. The mechanical behaviour of the soil is modelled by an elasto-plastic work hardening modified Cam- Clay constitutive model. A numerical solution for the theoretical formulation is presented. Standard finite element methods are used for spatial discretisation and finite difference methods are used for temporal discretisation. Verification of the model is achieved by means of programme of tests to check the following cryogenic components i) coupled thermo-hydraulic response, ii) deformation behaviour of the fully coupled thermo-hydro-mechanical model, iii) transient coupled liquid flow and deformation behaviour, and iv) latent heat of fusion. Validation focused on the impact of the cryogenic related processes included within the proposed theoretical formulation. In particular the development of ice lenses and the movement of moisture under cryogenic suction were investigated. The performance of the proposed model with respect to a number of variables was subsequently explored in order to determine their effect on the magnitude and growth of ice lenses in a freezing soil. The model was then applied to a large scale freezing experiment, namely a fully coupled thermo / hydro / mechanical simulation. The simulated results show a good correlation with the experimental results by predicting the patterns and trends of experimentally observed behaviour and the cryogenic processes that occur during the freezing and thawing of frost susceptible soils. It was therefore concluded that the proposed model is capable of providing a good representation of the fully coupled THM behaviour of saturated soils with cryogenic effects.
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Armonienė, Rita. "Freezing tolerance in winter wheat: gene identification and analysis". Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2014. http://vddb.library.lt/obj/LT-eLABa-0001:E.02~2014~D_20141208_113546-03867.
Testo completoAbstract (sommario):
Research objective: To identify new genes of winter wheat induced at low temperatures, to perform sequence analysis of these genes and to quantify their expression. Experimental tasks: 1. To evaluate freezing tolerance of various winter wheat genotypes under field and controlled conditions. 2. To identify differentially expressed genes at subsequent time points of cold acclimation and to perform analysis of their DNA sequences. 3. To optimize mutagenesis method and to create Targeting Induced Local Lesions in Genomes (TILLING) population of two winter wheat lines. 4. To identify mutations in differentially expressed genes by High Resolution melting (HRM) method, to estimate the impact of mutations on the gene expression during cold acclimation and tolerance to freezing.Tyrimų tikslas. Identifikuoti naujus žieminių kviečių genus, aktyvuojamus žemose temperatūrose bei atlikti šių genų sekų ir genetinės raiškos analizę. Tyrimų uždaviniai: 1. Ištirti žieminių kviečių genotipų tolerantiškumą žemoms neigiamoms temperatūroms natūraliomis ir dirbtinėmis sąlygomis. 2. Nustatyti skirtingose grūdinimosi stadijose diferenciškai ekspresuojamus genus (kDNR-AFLP analizė) ir atlikti DNR sekų analizę. 3. Optimizuoti mutagenezės metodą ir sukurti dviejų perspektyvių žieminių kviečių linijų mutagenines populiacijas. 4. Nustatyti skirtingu intensyvumu ekspresuojamų genų mutacijas HRM metodu, įvertinti nustatytų mutacijų įtaką genų ekspresijai grūdinimosi metu ir žemų neigiamų temperatūrų tolerancijai.
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Amarell, Martin [Verfasser]. "Ist Freezing of Gait ein systemisches Defizit? / Martin Amarell". Köln : Deutsche Zentralbibliothek für Medizin, 2018. http://d-nb.info/1160304793/34.
Testo completo
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Krause, Stefan, Pedro F. Aramendia, Daniela Täuber e Borczyskowski Christian von. "Freezing single molecule dynamics on interfaces and in polymers". Universitätsbibliothek Chemnitz, 2013. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-122254.
Testo completoAbstract (sommario):
Heterogeneous line broadening and spectral diffusion of the fluorescence emission spectra of perylene diimide molecules have been investigated by means of time dependent single molecule spectroscopy. The influence of temperature and environment has been studied and reveals strong correlation to spectral diffusion processes. We followed the freezing of the molecular mobility of quasi free molecules on the surface upon temperature lowering and by embedding into a poly(methyl methacrylate) (PMMA) polymer. Thereby changes of optical transition energies as a result of both intramolecular changes of conformation and external induced dynamics by the surrounding polymer matrix could be observed. Simulations of spectral fluctuations within a two-level system (TLS) model showed good agreement with the experimental findings.
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Al-Hakim, Kassem. "An investigation of spray-freezing and spray-freeze-dryings". Thesis, Loughborough University, 2004. https://dspace.lboro.ac.uk/2134/12935.
Testo completoAbstract (sommario):
Drying is an important process for a variety of industries such as pharmaceuticals, food, and chemicals, and produce products with low bulk density, good shelf stability, economical storage and transport, and in some cases unique structural qualities. Of the various drying methods available, freeze-drying is the most beneficial for heat sensitive products that susceptible to thermal degradation. Freezedrying also confers a porous structure on the material result from the voids left after subliming the ice crystals. Freeze-drying however is used mainly for high value products due to the high capital and operational costs. The cycle time of such a drier may take several hours. The spray-freeze-drying process has evolved in an attempt to shorten the freezedrying process time. The process atomises a liquid feed to increase the heat and mass transfer surface area. The spray is then frozen in a very cold gas or a cryogenic liquid to form solid particles, which are then freeze-dried. Some processes incorporate a - fluidised bed freeze-drier to reduce the drying time by forced convection heat and mass transfer. This project aim to develop the Spray Freeze- Drying process and examine the effect of the process on the drying entities and resulting product quality, followed by modelling of the spray freezing operation in an attempt to optimise the operation. This thesis is divided into two main areas of investigations; Spray freezing investigation as an influential on the resulting product size and structure. The experiments performed using Phase Doppler Anemometry technique to measure the particle size distributions and velocities in a specially constructed spray freezing chamber with incorporated windows. A spray freeze-drying chamber was constructed composed of three parts co-current spray freezing, gas - particle separation, and fluidisation freeze-drying unites. Successfully spray characterisation measurement was carried in both ambient and sub-ambient temperatures, producing data of the drop size distribution and velocities from refractive scattered laser PDA measurement. The technique produced valuable information about the spray size distribution and velocity, the application of this technique appear was a novel approach in the spray freezing process measurement. The result were used in the established spray freezing model derived from Pham (1984) freezing model incorporating with a recalescence stage from the Hindmarsh (2003) spray freezing model. The current model predicted the droplet freezing time, which is influenced by the droplet diameter, velocity and freezing gas temperature. The results also shows an agreement between the freezing time predicted and the PDA recognition of bursts rejected due to their possible phase change. The spray-freezing-drying chamber was operated in vacuum conditions to produce freeze-dried whey protein powder. The powder characteristic results shows an physical properties such as density, solubility and particle sizes in comparison to spray drying and cryo-spray freeze-drying. The morphology of the spray freeze-dried whey powder is substantially different to that produced by spray drying and displays a porous microstructure. The operation of the freeze-drying unites requires an further investigation for temperature, pressure, and flow control to maintain the freezedrying.
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Peters, Teresa Baker 1981. "Carbon dioxide flash-freezing applied to ice cream production". Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/35663.
Testo completoAbstract (sommario):
Includes bibliographical references (p. 62-64).Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2006.
(cont.) Carbon dioxide is recompressed from 1.97 x 106 Pa (285 psi) to 3.96 x 106 Pa (575 psi). The process is scaled by increasing the number of nozzles to accommodate the desired flow rate. Only 165 nozzles are required to flash freeze the ice cream mix at a 2000 L/hr ice cream production rate. The power consumption of a continuous cycle implementation is modeled including single or double stage carbon dioxide recovery and compression, pre-cooling of the carbon dioxide by a standard condensing unit, pumping of the ice cream mix at high pressure and extrusion of the ice cream powder by a piston or screw extruder. The power consumption of an implementation recovering 95% of the carbon dioxide is approximately 37.3% of the power consumption of a conventional process. The cost of the make-up carbon dioxide is $0.002 per liter of ice cream. A cart implementation is also possible.
Ice cream mix and other liquids are frozen by direct contact with carbon dioxide while carbon dioxide is throttled from a liquid phase to a saturated vapor phase. The process is demonstrated with a proof-of-principle apparatus that freezes discrete batches of mix. The fluid consumption, power consumption and space requirement of a continuous cycle implementation are modeled. In the proof-of-principle apparatus and the continuous cycle model, the ice cream mix is sprayed into the liquid carbon dioxide using 1.0 GPH Delavan fuel nozzles; the combined fluid is throttled by 2.0 GPH Delavan fuel nozzles, forming a fine mist during flash-freezing. The pressure at the outlet of the throttle determines the temperature of the saturated carbon dioxide vapor after the flashing process. The resulting product is a frozen carbonated ice cream powder. Depending on the implementation, 50-99% of the carbon dioxide flow is vented and can be compressed and recycled with additional make-up carbon dioxide flow. The required ratio of carbon dioxide to ice cream mix is found by balancing the change in enthalpy of each liquid from the inlet to the outlet state. For ice cream mix frozen from 5°C to -200C, the ratio is shown to be about 1.1.
by Teresa Susan Baker.
S.M.
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Krause, Stefan, Pedro F. Aramendia, Daniela Täuber e Borczyskowski Christian von. "Freezing single molecule dynamics on interfaces and in polymers". Physical Chemistry Chemical Physics. - 2011,13, S. 1754-1761, 2011. https://monarch.qucosa.de/id/qucosa%3A19944.
Testo completoAbstract (sommario):
Heterogeneous line broadening and spectral diffusion of the fluorescence emission spectra of perylene diimide molecules have been investigated by means of time dependent single molecule spectroscopy. The influence of temperature and environment has been studied and reveals strong correlation to spectral diffusion processes. We followed the freezing of the molecular mobility of quasi free molecules on the surface upon temperature lowering and by embedding into a poly(methyl methacrylate) (PMMA) polymer. Thereby changes of optical transition energies as a result of both intramolecular changes of conformation and external induced dynamics by the surrounding polymer matrix could be observed. Simulations of spectral fluctuations within a two-level system (TLS) model showed good agreement with the experimental findings.
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Xiao, Ruiyang. "The Freezing of Highly Sub-cooled H2O/D2O Droplets". The Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=osu1211567463.
Testo completo
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Cai, Hongchang. "Freezing of Palletized Food and Time-to-freeze Prediction". The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1563463782014162.
Testo completo
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Wang, Hongrui. "Developing Novel Methods to Mitigate Freezing Injury in Grapevines". The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1564743163557437.
Testo completo
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Robson, David J. "Physical aspects of cavitation and freezing in conifer xylem". Thesis, University of Aberdeen, 1986. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU362721.
Testo completoAbstract (sommario):
Part I details work on cavitation, refilling and permeability of conifer xylem. Part II shows how conifers may avoid widespread cavitation during freezing of the xylem sap. PART I Cavitation was induced in sapwood samples by sealing wood in semi-permeable membranes and immersion in osmotic solutions. Emptying of up to 20-30% of the tracheids occurred for absolute pressures of between 1.0 x 105 N. m-2and -4 x 105 N m-2but very little further emptying occurred when the pressure was lowered to -9 x 105 N m-2. The limit of emptying found for this range of pressures indicates that one type of tracheid (earlywood or latewood) preferentially cavitates. It is suggested that the latewood cavitates more readily than the earlywood. Experimental tests showed that widespread refilling of cavitated tracheids only occurred when the xylem sap pressure was raised above the pressure in the cavitated tracheid lumens. Six theories to explain refilling of tracheids at the top of tall trees are considered. Of these capillary condensation, root pressure, refilling by ray parenchyma cells and capillarity are discarded on theoretical grounds. Experiments showed that temperature changes and temperature gradients did not cause refilling in equilibrated samples or in intact stem and root systems. Water absorption at the leaves appears to be the most likely method of refilling. Steady state liquid permeability measurements showed that xylem permeability decreased exponentially with increasing void volume for Douglas fir and Sitka spruce. The curves are probably not applicable to living trees because some liquid flowed through partially refilled tracheids. PART II Pressure rises up to 39 x 105 N m-2 and low freezing rates (1.75 to 2.3 pm s-1) were measured in freezing sapwood samples using implanted pressure transducers and thermistors. Electron micrographs of slowly frozen wood show bordered pit aspiration is not widespread during radial freezing. A finite element model of freezing in a single tracheid predicts pressure rises similar to those measured experimentally. This model also predicts that 5 to 8% of the water in the lumen migrates to other areas during freezing. However, in contradiction to experimental results, a model of whole stem freezing predicts freezing rates four times faster than the measured values. The low freezing rates measured experimentally indicate that bubbles only nucleate in the outermost layers of the xylem during freezing. However, if 5 to 8% of the lumen water migrates during freezing, low pressures on thawing may still cause cavitation. For this to be avoided it is suggested that water migrates from freezing tracheids to already frozen tracheids through narrow cell wall capillaries.
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Shah, Ketan R. Carleton University Dissertation Engineering Civil. "Deformations and stresses in pipelines buried in freezing ground". Ottawa, 1990.
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Goh, Lina. "Freezing of gait in Parkinson’s disease: rehabilitation and measurement". Thesis, The University of Sydney, 2022. https://hdl.handle.net/2123/29693.
Testo completoAbstract (sommario):
This thesis presents three studies: (1) a systematic review with meta-analyses that evaluates the effects of rehabilitation interventions on freezing of gait in people with Parkinson’s disease; (2) a pilot trial that examines the feasibility and acceptability of a video self-modelling intervention to address freezing of gait; and (3) a study that explores the reliability, validity, and usability of the Ziegler test to measure freezing of gait severity. In study 1, results from meta-analyses show a small effect of physiotherapy/exercise on reducing freezing of gait post-intervention (Hedges’ g=-0.26, 95% CI -0.38 to -0.14), consistent with previous reviews. However, the robust methodology used in study 1 suggests cautious interpretation as the certainty of the evidence is very low and intervention effects are unlikely to be clinically meaningful. It is likely that a comprehensive assessment of freezing of gait triggers and prescription of personalised interventions that is sustained over time will be most effective at addressing freezing of gait. In study 2, evaluation of personalised video self-modelling (delivered via a virtual reality headset) plus physical practice of movement strategies, was shown to be both feasible and acceptable, with 90% retention, 84% adherence to video viewing and most reporting they would use the intervention again. In study 3, the Ziegler test was shown to be a reliable (ICC2,1=0.80; ICC3,1=0.91) and valid freezing of gait severity measure when used by physiotherapists in real time. The Ziegler test duration may also be used as a proxy measure for freezing of gait severity. Taken together, these results help researchers and clinicians determine effective personalised interventions to reduce freezing of gait and improve measurement of freezing of gait severity by using quantitative tools. Reducing freezing of gait could improve mobility, reduce fall risk, and increase health-related quality of life in people with Parkinson’s disease.
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Sun, Renfei. "Attention Network for Video Based Freezing of Gait Detection". Thesis, The University of Sydney, 2022. https://hdl.handle.net/2123/28908.
Testo completoAbstract (sommario):
Freezing of gait (FoG) is a typical symptom of Parkinson's disease (PD), which is a brief, episodic absence or marked reduction despite the patients' intention of walking.
It is important to timely identify FoG events for clinical assessments. However, well-trained experts are required to identify FoG events, which is subjective and time-consuming.
Therefore, automatic FoG identification methods are highly demanded. In this study, we address this task as a human action detection problem based on vision inputs. Two novel attention based deep learning architectures, namely convolutional 3D attention network (C3DAN) and higher order polynomial transformer (HP-Transformer), are proposed to investigate fine-grained FoG patterns.
The C3DAN addresses the FoG detection task by exploring the appearance features in detail to learn an informative region for more effective detection. The network consists of two main parts: Spatial Attention Network (SAN) and 3-dimensional convolutional network (C3D). SAN aims to generate an attention regions from coarse to fine, while C3D extracts discriminative features. Our proposed approach is able to localize attention region without manual annotation and to extract discriminative features in an end-to-end way.
The HP-Transformer incorporates pose and appearance feature sequences to formulate fine-grained FoG patterns. In particular, higher order self-attentions are proposed based on higher order polynomials. To this end, linear, bilinear and trilinear transformers are formulated in pursuit of discriminative fine-grained representations. These representations are treated as multiple streams and further fused by a self-attention based fusion strategy for FoG detection.
Comprehensive experiments on a large in-house dataset collected during clinical assessments demonstrate the effectiveness of the proposed methods. The two methods both achieved promising results and in particular, the HP-Transformer achieved an AUC of 0.92 in the FoG detection task.
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Anhuaman, Laura Andrea Leon. "Fatores comportamentais, hormonais e neuroanatômicos associados à vulnerabilidade ao estresse em ratos Carioca High Conditioned-Freezing (CHF) e Carioca Low Conditioned-Freezing (CLF)". Universidade de São Paulo, 2014. http://www.teses.usp.br/teses/disponiveis/59/59134/tde-03042014-174324/.
Testo completoAbstract (sommario):
A ansiedade e a depressão são as condições psicopatológicas mais comuns na atualidade. As pesquisas científicas em neurociência, psicologia, psiquiatria e medicina geral procuram encontrar diferentes formas para o tratamento e prevenção. No entanto, a maioria das pesquisas não leva em conta as diferenças individuais ou história do individuo. Quase toda a investigação farmacológica é feita em populações heterogêneas de animais, conduzindo assim à \"média\" dos dados. Recentemente, no Laboratório de Neurociência Comportamental na Pontifícia Universidade Católica do Rio de Janeiro (PUC-RJ), duas novas linhagens de ratos Wistar foram selecionadas fenotipicamente da resposta emocional de congelamento em um teste de medo condicionado . Uma das linhagens, denominada Carioca High ConditionedFreezing (CHF), apresenta uma resposta significativamente aumentada de congelamento no teste, enquanto que a outra (Carioca Low Conditioned-Freezing, CLF) mostra uma resposta de congelamento baixa. Em todos os experimentos utilizamos a linhagem controle (Random, RND) Wistar resultado de cruzamento aleatório entre ratos Wistar. Aqui apresentamos dados de diversos experimentos que avaliaram as diferenças em condições basais e vulnerabilidade ao estresse entre as duas linhagens e a linhagem RND. A concentração plasmática de corticosterona dos ratos foi comparada entre as duas linhagens e o grupo RND, primeiramente no nível basal e posteriormente após a exposição ao mesmo teste, onde foram expostos ao medo condicionado, como estímulo aversivo. Também foi avaliada a proliferação celular e sobrevivência. A imuno-histoquímica para c-fos foi conduzida com o objetivo de se determinar as diferenças de atividade neural entre as duas linhagens e o grupo RND. Um teste farmacológico com ketanserina, antagonista 5-HT2A, foi realizado e os animais foram avaliados quanto à ansiedade e locomoção, no labirinto em cruz elevado. Todos os nossos resultados mostraram diferenças estatisticamente significativas entre as linhagens selecionadas. Estes resultados sugerem que as diferentes condições basais podem ter impacto sobre a reação de comportamento exibido por cada animal. Assim, o uso de grupos selecionados é melhor para se modelar transtornos de ansiedade e procurar quais são caraterísticas que protegem aos animais que não apresentam os sintomas modelados. A partir dos nossos resultados foi evidente que os perfis comportamentais e neuroquímicos dos três grupos CHF, CLF e RND foram qualitativamente e quantitativamente diferentes. Na linha de base após ser fenotipados foi observado que existem diferenças na proliferação celular. Após a reexposição ao contexto observaram-se diferenças na concentração de corticosterona e na ativação neuronal. O estresse crônico levou a respostas diferenciais no número de neurônios imaturos, e o teste farmacológico levou a respostas diferencias tanto a nível local como sistêmico. Os dados obtidos podem ajudar a um melhor entendimento às bases neurobiológicas de aspectos associados às psicopatologias como ansiedade e depressão que estão relacionadas com a vulnerabilidade ao estresse.Anxiety and depression are the most common psychopathological conditions today. Scientific research in neuroscience, psychology, psychiatry and general medicine seeks to find different ways for treatment and prevention. However, most research does not take into account individual differences and history. Almost all pharmacological research is done in heterogeneous populations of animals, thereby leading to the \"average\" data. Recently, in the Laboratory of Behavioral Neuroscience at the Pontifical Catholic University of Rio de Janeiro (PUC - RJ), two new strains of rats were selected phenotypically by their emotional response (freezing) in a test of cond itioned fear. One of the lines, so called \"Carioca High Conditioned - Freezing\" (CHF) has an increased freezing in the test , whereas the other (\"Carioca Low -Conditioned Freezing \" CLF) shows low freezing response . In all experiments we used the Wistar control strain (RND) derived from random bred between Wistar rats. Here we present data from several experiments evaluating the differences in basal conditions and vulnerability to stress between the two strains and RND strain. The plasma corticosterone of rats was compared between the two lines and the RND group, first at baseline and then after exposure to the same test where the y were exposed to conditioned fear as aversive stimulus. We also analyzed the cell proliferation and survival in the hippocampus after chronic stress. Immunohistochemistry for c -fos was conducted in order to determine the differences in neural activity between the two strains and the RND group. A pharmacological test with ketanserin, 5 -HT2A antagonist, was performed and the animals were assessed for anxiety and locomotion in the elevated plus maze. All our results showed statistically significant differences between the selected strains. These results suggest that different baseline conditions may have an impact on the behavior exhibited by each animal. Thus the use of selected groups is better approach in order to model anxiety disorders and to determine which features prevent animal from presenting symptoms. It is evident that the neurochemical and behavioral profiles of the three groups CHF, CLF and RND were different qualitatively and quantitatively. At baseline after been phenotyped it has been observed that there are differences in cell proliferation and corticosterone concentration. After re-exposure to the context differences were observed in the concentration of corticosterone and neuronal activation. Chronic stress has led to differential responses in the number of immature neurons. And the pharmacological test led to differential responses at both local and systemic. The data obtained are useful for a better understanding of the neurobiological aspects associated with psychopathologies such as anxiety and depression that are associated with vulnerability to stress.