Évaluation de la capacité du canal UWB minier

La capacité du canal permet de caractériser les performances maximales d’un canal de transmission, le nombre maximal de bits susceptible d’être transmis par seconde. Pour un canal donné, l’UWB peut garantir un grand débit pour la transmission de données. Le canal de transmission UWB est généralement un canal à trajets multiples, surtout pour les applications à l’intérieur. Aussi, la réponse de ce canal est sélective dans le domaine fréquentiel. Pour étudier la capacité de n’importe quel canal il faut d’abord le caractériser et le modéliser. Dans notre recherche, on va se baser sur les mesures faites par Chehri et Fortier dans la mine CANMET à Val-d’Or qui est située à 500 km au nord de Montréal, Canada. Ces mesures montrent que la distribution Nakagami donne un bon ajustement pour l’amplitude du signal reçue à petit échelle. La formule classique de la capacité de Shannon est obtenue pour les canaux ayant des réponses fréquentielles plates. Cette formule ne s’applique pas directement dans notre modèle de canal. Pour utiliser la formule classique de la capacité de Shannon, nous devons d’abord diviser la bande de fréquences en un nombre très grand (théoriquement infini) de petites bandes, considérées comme des sous-canaux à réponse plates dans le domaine fréquentiel. Ensuite, on peut appliquer une distribution optimale de puissance maximisant la capacité pour une puissance d’émission totale limitée. Cette méthode est connue sous le nom de "waterfilling". Les travaux antérieurs sur l’évaluation de la capacité du canal UWB en externe (outdoor) n’ont pas tenu compte des évanouissements du canal, et en interne (indoor), le cas d’un milieu UWB minier n’a pas encore été abordé. Dans ce mémoire de maîtrise on s’est particulièrement intéressé au problème d’évaluation de la capacité du canal UWB minier. En utilisant la méthode "waterfilling" on a calculé la capacité d’un canal UWB minier d’une manière optimale en tenant compte des caractéristiques d’évanouissement du canal. Les résultats obtenus prouvent la pertinence de la méthode "waterfilling" dans ces type des canaux ; cette méthode donne une amélioration importante de la capacité, d’un facteur entre 1.1 à 1.22 fois plus grand que la capacité uniforme lorsque le SNR 40 dB, la capacité optimale et la capacité uniforme convergent, et on remarque que les deux méthodes donnent les mêmes résultats lorsque le rapport signal sur bruit est grand (> 80 dB). Capacity plays an important role in characterizing the maximum performance for channel transmission by providing the maximum number of bits that can be transmitted per second. Furthermore, for a given channel, a large rate for data transmission can be guaranteed using UWB modulation. In fact, the UWB transmission channel is generally a multipath channel especially for indoor applications. Thus, the channel response is selective in the frequency domain. To be able to study the capacity of any channel, it should be characterized and modeled. In this research, we depend on the measures taken by Chehri and Fortier in the CANMET mine in Val-d’Or, located 500 km north of Montreal, Canada. These measurements show that the Nakagami distribution gives a good adjustment for the amplitude of the signal received at a small scale. Indeed, the classical formula for the Shannon capacity is used for flat channels. Thus, we can first divide the whole frequency band into many small bands, in which the sub-channel can be considered frequency-flat. After that, we can apply an optimal distribution of power to maximize the capacity of total transmission over limited power; this method is known as "waterfilling". Previous works on the evaluation of UWB channel capacity considered the external (outdoor) case, however, they did not consider the fading channel. Also, the internal (indoor) studies did not discuss the case of the mining channel. In this thesis, we paid particular attention to the problem of evaluating the UWB channel in the mine. By using the "waterfilling" method, we calculated the capacity of a UWB channel mining optimally, taking into account the characteristics of the fading channel. The results demonstrate the relevance of the "waterfilling" method in these types of channels. We show that, when the transmitted signal-to-noise ratio (SNR) is lower than 40 dB, using optimal power spectrum allocation at the transmitter side can increase transmission rate compared to the uniform power spectrum allocation scheme. Whereas, when the transmitted SNR is higher than 80 dB, the benefit of optimal power spectrum allocation is very limited

Oncometabolites:linking altered metabolism with cancer

The discovery of cancer-associated mutations in genes encoding key metabolic enzymes has provided a direct link between altered metabolism and cancer. Advances in mass spectrometry and nuclear magnetic resonance technologies have facilitated high-resolution metabolite profiling of cells and tumors and identified the accumulation of metabolites associated with specific gene defects. Here we review the potential roles of such "oncometabolites" in tumor evolution and as clinical biomarkers for the detection of cancers characterized by metabolic dysregulation

Characterization of metabolites in infiltrating gliomas using ex vivo &supl;H high-resolution magic angle spinning spectroscopy.

Gliomas are routinely graded according to histopathological criteria established by the World Health Organization. Although this classification can be used to understand some of the variance in the clinical outcome of patients, there is still substantial heterogeneity within and between lesions of the same grade. This study evaluated image-guided tissue samples acquired from a large cohort of patients presenting with either new or recurrent gliomas of grades II-IV using ex vivo proton high-resolution magic angle spinning spectroscopy. The quantification of metabolite levels revealed several discrete profiles associated with primary glioma subtypes, as well as secondary subtypes that had undergone transformation to a higher grade at the time of recurrence. Statistical modeling further demonstrated that these metabolomic profiles could be differentially classified with respect to pathological grading and inter-grade conversions. Importantly, the myo-inositol to total choline index allowed for a separation of recurrent low-grade gliomas on different pathological trajectories, the heightened ratio of phosphocholine to glycerophosphocholine uniformly characterized several forms of glioblastoma multiforme, and the onco-metabolite D-2-hydroxyglutarate was shown to help distinguish secondary from primary grade IV glioma, as well as grade II and III from grade IV glioma. These data provide evidence that metabolite levels are of interest in the assessment of both intra-grade and intra-lesional malignancy. Such information could be used to enhance the diagnostic specificity of in vivo spectroscopy and to aid in the selection of the most appropriate therapy for individual patients

Metabolic Profiling of IDH Mutation and Malignant Progression in Infiltrating Glioma.

Infiltrating low grade gliomas (LGGs) are heterogeneous in their behavior and the strategies used for clinical management are highly variable. A key factor in clinical decision-making is that patients with mutations in the isocitrate dehydrogenase 1 and 2 (IDH1/2) oncogenes are more likely to have a favorable outcome and be sensitive to treatment. Because of their relatively long overall median survival, more aggressive treatments are typically reserved for patients that have undergone malignant progression (MP) to an anaplastic glioma or secondary glioblastoma (GBM). In the current study, ex vivo metabolic profiles of image-guided tissue samples obtained from patients with newly diagnosed and recurrent LGG were investigated using proton high-resolution magic angle spinning spectroscopy (1H HR-MAS). Distinct spectral profiles were observed for lesions with IDH-mutated genotypes, between astrocytoma and oligodendroglioma histologies, as well as for tumors that had undergone MP. Levels of 2-hydroxyglutarate (2HG) were correlated with increased mitotic activity, axonal disruption, vascular neoplasia, and with several brain metabolites including the choline species, glutamate, glutathione, and GABA. The information obtained in this study may be used to develop strategies for in vivo characterization of infiltrative glioma, in order to improve disease stratification and to assist in monitoring response to therapy

Nuclear Magnetic Resonance metabolomics reveals an excretory metabolic signature of renal cell carcinoma

RCC usually develops and progresses asymptomatically and, when detected, it is frequently at advanced stages and metastatic, entailing a dismal prognosis. Therefore, there is an obvious demand for new strategies enabling an earlier diagnosis. The importance of metabolic rearrangements for carcinogenesis unlocked a new approach for cancer research, catalyzing the increased use of metabolomics. The present study aimed the NMR metabolic profiling of RCC in urine samples from a cohort of RCC patients (n = 42) and controls (n = 49). The methodology entailed variable selection of the spectra in tandem with multivariate analysis and validation procedures. The retrieval of a disease signature was preceded by a systematic evaluation of the impacts of subject age, gender, BMI, and smoking habits. The impact of confounders on the urine metabolomics profile of this population is residual compared to that of RCC. A 32-metabolite/resonance signature descriptive of RCC was unveiled, successfully distinguishing RCC patients from controls in principal component analysis. This work demonstrates the value of a systematic metabolomics workflow for the identification of robust urinary metabolic biomarkers of RCC. Future studies should entail the validation of the 32-metabolite/resonance signature found for RCC in independent cohorts, as well as biological validation of the putative hypotheses advanced

Application of MR Spectroscopic Techniques for the Development and Translation of Metabolite Markers Characterizing Infiltrating Glioma

Despite ever more advanced characterization, the family of malignant central nervous system diseases known as infiltrating glioma remain pernicious and resistant to treatment. Because of their molecular and pathologic heterogeneity, they are among the most complex cancers in adults, with tremendous variability in patient outcomes being observed across oncologic subtypes. Over the course of therapy, magnetic resonance imaging (MRI) is critical to evaluating the level of response as the diagnostic standard for clinical management. Conventional MRI, having superior soft tissue contrast, provides a non-invasive means of detecting abnormalities that are embedded within neural anatomy. However, gauging the full extent of tumor is difficult owing to non-specific changes, which may either reflect benign processes in the aftermath of treatment or tumor infiltration. Given the ambiguity associated with anatomical imaging, magnetic resonance spectroscopy (MRS) has emerged as a technique that can add diagnostic value to clinical practice by probing signature chemical species characterizing disease. The primary focus of this work was the development of translatable biomarkers for infiltrating glioma using analogous ex vivo methodology that has greater sensitivity and spectral resolution. By analyzing image-guided tissue samples acquired from a large cohort of patients with pathologically distinct subtypes, it was possible to characterize metabolite expression across diverse swathes of tumor representing natural heterogeneity. Quantified data revealed distinct metabolomic profiles for each of the clinically relevant subtypes that enabled their differential classification. Importantly, classification models were able to predict malignant progression on the basis of these profiles, highlighting the potential to determine pathologic trajectory. Separate analysis of contrast-based radiographic subtypes of the most aggressive form of glioma demonstrated unique metabolite expression in the portion of tumor that fails to exhibit contrast and is therefore masked on standard imaging.Since some of the metabolite markers discovered exhibited features that diminished the lifetime of their signal, technical development of an in vivo MRS sequence was also undertaken. The creation of radiofrequency (RF) pulses with reduced peak power requirements was critical to the design of the sequence and enabled improved signal fidelity over longer acquisition times when incorporated into existing frameworks. Results from this project and those obtained ex vivo support greater clinical integration of spectroscopy