Antarctic Ice Sheet and Radar Altimetry: A Review

Altimetry is probably one of the most powerful tools for ice sheet observation. Our vision of the Antarctic ice sheet has been deeply transformed since the launch of the ERS1 satellite in 1991. With the launch of ERS2 and Envisat, the series of altimetric observations now provides 19 years of continuous and homogeneous observations that allow monitoring of the shape and volume of ice sheets. The topography deduced from altimetry is one of the relevant parameters revealing the processes acting on ice sheet. Moreover, altimeter also provides other parameters such as backscatter and waveform shape that give information on the surface roughness or snow pack characteristics

Chromosomal and functional characterization of the early stages of human embryogenesis

The main objective of modern IVF is to maximize the effectiveness of the times to achieve a pregnancy and at the same time also manage the risks, looking for new predictive parameters of the embryonic developmental competence. The analysis of embryo morphodynamic growth is not associated with its euploidy or implantation competence. However, some static parameters of embryo quality might exist that could be associated with embryo competence beyond its chromosomal constitution. The aims of this project are: i) To study from a morphodynamic, genetic and clinical point of view, embryos that show an abnormal development during preimplantation growth, in particular, the exclusion of cells (ExC) from embryonic mass at the moment of morulation. ii) Trying to understand if the morphodynamic characterization of euploid blastocyst development allows a higher prediction of live-birth (LB) after single-embryo-transfers (SET). For both the aims set in this Ph.D. project, preimplantation development and morphodynamic growth of embryos were observed in a time-lapse culture system (Embryoscope, Vitrolife). For the first aim, our preliminary data show that the exclusion of cells from the body of the blastocyst could be not-intuitively associated to a higher competence resulting from the embryonic capacity to overcome an abnormal cleavage pattern occurred in the very first divisions before the activation of the embryonic genome (4 to 8cell stage in humans). It is exciting the future perspective of collecting the ExC aiming at analyzing them through the karyomapping technology as well as biochemical assays, to better describe both the chromosomal segregation and the cellular physiology. For the second aim, we have divided the study into two phases in collaboration with 3 IVF Centers. In phase1, 511 first euploid SETs from 1069 patients undergoing preimplantation-genetic-testing-for-aneuploidies (PGT-A) cycles at 2 IVF centers were investigated (training set). All embryos were cultured in a specific time-lapse incubator with continuous media. The data from the time of polar-body-extrusion to time starting-blastulation were collected. Trophectoderm (TE) and inner-cell-mass (ICM) static morphology were also assessed. Logistic regressions were conducted to outline a predictive model of LB, whose power was estimated through a ROC-curve. In phase2, this model was tested in an independent dataset of 319 consecutive SETs from 546 PGT-A cycles at 3 IVF centers (validation set). The average LB-rate in the training set was 40% (N=207/511). Only time-of-morulation (tM) and trophectoderm quality were outlined as putative predictors of LB at both centers. The model showed a significant AUC (area under the curve) of 0.65. In the validation set, the euploid blastocysts characterized by tM<80hr and high-quality trophectoderm resulted in an LB-rate of 55.2% (n=37/67), while those with tM≥80hr and a low-quality trophectoderm resulted in an LB-rate of 25.5% (N=13/51;p<0.01). The ROC-curve analysis pictured an AUC of 0.6. A model including tM and trophectoderm quality involves a better prediction of euploid blastocyst reproductive competence. This model was reproducible across different centers under specific culture conditions. These data support the crucial role of morulation for embryo development, a stage that involves massive morphological, cellular and molecular changes requiring more investigations. Moreover, important guidelines for IVF laboratories that do not conduct a time-lapse-based embryo culture may arise from these two studies

OLIGODENDROCYTE 2PHATAL REVEALS DYNAMICS OF MYELIN DEGENERATION AND REPAIR

Oligodendrocytes are responsible for producing myelin in the central nervous system. This lipid-rich coating along axons helps to increase action potential velocity, provide metabolic support to axons, and facilitate fine-tuning of neuronal circuitry. Demyelination and/or myelin dysfunction is widespread in neurodegenerative diseases and aging. Despite this, we know very little about how individual oligodendrocytes, or the myelin sheaths they produce, degenerate. Myelin repair, carried out by resident oligodendrocyte precursor cells (OPCs), is known to occur following myelin damage in certain contexts. We sought to investigate the cellular dynamics of oligodendrocyte degeneration and repair by developing a non-inflammatory demyelination model, combining intravital imaging with a single-cell ablation technique called 2Phatal. Oligodendrocyte 2Phatal activated a stereotyped degeneration cascade which triggered remyelination by local OPCs. Remyelination efficiency was dependent on initial myelin patterns and dynamic imaging revealed rapid repair with near-seamless transitions between myelin loss and remyelination, a process we call synchronous remyelination. A subset of highly branched OPCs executed this remyelination, pointing towards demyelination-associated morphological signatures of fate. Age-related demyelination mirrored the degenerative cascade observed with 2Phatal; however, remyelination in aging was defective due to failed oligodendrogenesis. Thus, oligodendrocyte 2Phatal uncovered novel forms of rapid remyelination that restore myelin patterns in the adult but are absent in aging. We go on to demonstrate that the maturation state of oligodendrocytes determines the dynamics and mechanism of cell death. Premyelinating and newly formed oligodendrocytes degenerate more rapidly than mature oligodendrocytes, but faster than OPCs, following 2Phatal. Furthermore, they appear to utilize a caspase-dependent form of cell death, while mature oligodendrocytes do not. This new insight suggests that different cell death mechanisms are used by these two populations, necessitating distinct strategies to protect preestablished and new oligodendrocytes in human aging and/or disease

Audio Signal Processing Using Time-Frequency Approaches: Coding, Classification, Fingerprinting, and Watermarking

Audio signals are information rich nonstationary signals that play an important role in our day-to-day communication, perception of environment, and entertainment. Due to its non-stationary nature, time- or frequency-only approaches are inadequate in analyzing these signals. A joint time-frequency (TF) approach would be a better choice to efficiently process these signals. In this digital era, compression, intelligent indexing for content-based retrieval, classification, and protection of digital audio content are few of the areas that encapsulate a majority of the audio signal processing applications. In this paper, we present a comprehensive array of TF methodologies that successfully address applications in all of the above mentioned areas. A TF-based audio coding scheme with novel psychoacoustics model, music classification, audio classification of environmental sounds, audio fingerprinting, and audio watermarking will be presented to demonstrate the advantages of using time-frequency approaches in analyzing and extracting information from audio signals.</p