Terahertz Desorption Emission Spectroscopy

Enhancing our understanding of the formation and evolution of the Universe is strongly dependent upon the observation of matter that exists between the stars and that forms the interstellar medium (ISM). Using Radio-telescopes based on heterodyne detection (such as ALMA), nearly 200 molecules have been detected. Whilst molecules, such as H2O and CH3OH, can only form in the solid state, the formation of complex organic molecules is not fully known. Moreover many simple species desorb from ices during the star formation process being useful tracers of these astronomical processes, but only if the thermal and non-thermal desorption mechanisms are fully understood. In this thesis, I have designed, developed, built and proven a new experimental technique, namely Terahertz Desorption Emission Spectroscopy (THz-DES). The basis of THz-DES is to recreate the chemical conditions found in interstellar environments by emulating the astronomical detection techniques. The emission spectroscopy is based on the integration of a total-power Schottky-barrier based radiometer operating between 320-350 GHz (overlapping with ALMA band 7), coupled to a vacuum chamber where interstellar ice analogues can be grown on a 77 K cold-finger, then thermally desorbed, enabling the gas-ice synergy to identify molecular spectra and desorption energies. I demonstrate the versatility of the technique observing thermal desorption from pure, layered or mixed ices of nitrous oxide, water and methanol. The results are compared to existing literature values of the desorption energies, and the known spectral features. Finally, there is some evidence that certain energy levels of desorbing species are under-populated relative to the population expected in local thermodynamic equilibrium conditions. This impact of surface constrains on the dynamics and internal energy of desorbing molecules, largely ignored in astronomy, shows interesting promise for the future of the THz-DES technique

Dual-Polarised Radiometer for Road Surface Characterisation

This paper presents measurements using a dual-polarised radiometer operating at 93\ua0GHz to detect ice or water on asphalt in laboratory conditions. The brightness temperatures of both H and V polarizations were measured for a dry surface, liquid water, and ice on asphalt at observation angles of 50\ub0 and 56\ub0. The results presented in this paper demonstrate that the studied road conditions can be identified by the radiometer. The measurements are compared with a model and surface parameters, such as dielectric constant and roughness are fitted and compared to reference values. The experiments and results, described in this article, are the first steps towards the future installation of a polarimetric sensor on a moving vehicle for traffic safety

Road Surface Characterization Using a Radiometer at 100 GHz

A dual polarization super-heterodyne radiometer operating between 85 and 100 GHz has been developed and used for surface characterization. The instrument can detect changes from dry to icy road in many environmental conditions (night, fog, rain) by measuring the combination of reflected/transmitted radiation from the surface at two orthogonal polarizations. The difference in brightness temperature between those polarizations is an accurate tool to distinguish ice from dry road surfaces. Results from measurement of dry asphalt and ice layers on asphalt are presented in this paper

Oil, water, and ice detection on road surfaces with a millimeter-wave radiometer

Passive radiometers are well-known instruments used in the characterization of soil, sea surfaces and remote sensing of the earth atmosphere with satellites or airplanes. The instrument described in this article is a dual-polarised superheterodyne radiometer operating around 93 GHz. It is placed on a structure to measure road surface conditions (ice, water or oil) in a laboratory-controlled environment. This radiometer measures the reflected and emitted radiations from the road surface (asphalt and concrete) and the background temperature, in two orthogonal polarizations (H and V). The difference in the dielectric properties of the ice, oil and water from dry road surface allows to distinguish them efficiently. This kind of technique can be used for road surface recognition in all weather conditions and does not require presence of daylight or other sources of illumination. In this paper, calibration procedures and radiometric characterisations of the radiometer are studied in order to select the best and simpler method to operate the radiometer. It was found that calibrating the radiometer with only one blackbody target or using a table of gain and system noise temperature is sufficiently accurate over a long time to be able to distinguish dry from ice or water covered surfaces. The laboratory results are showing a high difference in the brightness temperature between road surface covered with ice, water or oil and the dry road surface. No ambiguities between those conditions exist but potential limitations could rise, for example if the road surface roughness changes during a measurement. Those promising results validate the potential of using radiometer for road safety and the automotive industry. The presented laboratory measurements are the first step towards the implementation of the instrument into a moving vehicle for alerting drivers ahead of unforeseen dangers.Downloading of the abstract is permitted for personal use only

TeraHertz Desorption Emission Spectroscopy (THz DES) of space relevant ices

We present an experimental instrument that performs laboratory-based gas-phase Terahertz Desorption Emission Spectroscopy (THz-DES) experiments in support of astrochemistry. The measurement system combines a terahertz heterodyne radiometer that uses room temperature semiconductor mixer diode technology previously developed for the purposes of Earth observation, with a high-vacuum desorption gas cell and high-speed digital sampling circuitry to enable high spectral and temporal resolution spectroscopy of molecular species with thermal discrimination. During use, molecules are condensed on to a liquid nitrogen cooled metal finger to emulate ice structures that may be present in space. Following deposition, thermal desorption is controlled and initiated by means of a heater and monitored via a temperature sensor. The ‘rest frequency’ spectral signatures of molecules released into the vacuum cell environment are detected by the heterodyne radiometer in real-time and characterised with high spectral resolution. To demonstrate the viability of the instrument, we have studied Nitrous Oxide (N2O). This molecule strongly emits within the terahertz (sub-millimetre wavelength) range and provide a suitable test gas and we compare the results obtained with more traditional techniques such as quadrupole mass spectrometry. The results obtained allow us to fully characterize the measurement method and we discuss its potential use as a laboratory tool in support of astrochemical observations of molecular species in the interstellar medium and the Solar System

The role of terahertz and far-IR spectroscopy in understanding the formation and evolution of interstellar prebiotic molecules

Stellar systems are often formed through the collapse of dense molecular clouds which, in turn, return copious amounts of atomic and molecular material to the interstellar medium. An in-depth understanding of chemical evolution during this cyclic interaction between the stars and the interstellar medium is at the heart of astrochemistry. Systematic chemical composition changes as interstellar clouds evolve from the diffuse stage to dense, quiescent molecular clouds to star-forming regions and proto-planetary disks further enrich the molecular diversity leading to the evolution of ever more complex molecules. In particular, the icy mantles formed on interstellar dust grains and their irradiation are thought to be the origin of many of the observed molecules, including those that are deemed to be ‘prebiotic’; that is those molecules necessary for the origin of life. This review will discuss both observational (e.g., ALMA, SOFIA, Herschel) and laboratory investigations using terahertz and far-IR (THz/F-IR) spectroscopy, as well as centimeter and millimeter spectroscopies, and the role that they play in contributing to our understanding of the formation of prebiotic molecules. Mid-IR spectroscopy has typically been the primary tool used in laboratory studies, particularly those concerned with interstellar ice analogues. However, THz/F-IR spectroscopy offers an additional and complementary approach in that it provides the ability to investigate intermolecular interactions compared to the intramolecular modes available in the mid-IR. THz/F-IR spectroscopy is still somewhat under-utilized, but with the additional capability it brings, its popularity is likely to significantly increase in the near future. This review will discuss the strengths and limitations of such methods, and will also provide some suggestions on future research areas that should be pursued in the coming decade exploiting both space-borne and laboratory facilities

Gender effect on driving cessation in pre-dementia and dementia phases: results of the 3C population-based study

Objectives: Aging entails deterioration in sensory, physical, and cognitive functions, raising doubt in the driving capacity of older drivers, especially when the deficits are severe, as in dementia. Many older drivers, especially women, adapt their driving habits in order to compensate for these deficits and eventually stop driving. The present prospective study assessed driving cessation in men and women throughout the dementia process, including a 2-year pre-dementia phase. Methods: The study was based on a three-city cohort of subjects who were aged 65 years and older in 2000 and followed for more than 10 years. Active dementia detection was conducted at each followup. The probability of driving cessation was assessed in men and women during the 2-year predementia phase and until 5 years after diagnosis. Results: In the 2-year pre-dementia phase, both men and women ceased driving earlier than drivers with no central nervous system pathology (pLa conduite automobile est une activité de la vie quotidienne complexe qui nécessite des capacités visuelles, motrices, et cognitives. Il existe au cours du vieillissement normal une baisse légère de ces capacités. Au plan cognitif on note un ralentissement de la vitesse de traitement de l'information et des perturbations des processus attentionnels qui vont s'aggraver chez les personnes atteintes de pathologies cérébrales. Face à ces modifications, beaucoup de conducteurs âgés modifient leurs habitudes de conduite, en particulier les femmes, mais l'arrêt de la conduite reste une étape parfois difficile à franchir. L'étude proposée estime la probabilité d'arrêt de la conduite au cours du processus démentiel, incluant la phase pré-démentielle. Elle repose sur la cohorte des 3Cités, avec 7203 titulaires du permis de conduire âgés de 65 ans et plus. A l'inclusion et à chaque suivi, les participants suspectés de démence suite à l'évaluation neuropsychologique sont examinés par un comité de neurologues et gériatres qui confirment le diagnostic selon les critères du DSM IV. Au cours des 10 ans de suivi, 512 titulaires du permis ont eu un diagnostic de démence. Cette procédure permet aussi d'identifier des personnes non démentes à un suivi et qui remplissent les critères de démence 2.5 ans plus tard, les « futurs déments ». Dans la phase pré-démentielle, les personnes cessent de conduire plus tôt que celles qui ne présentent pas de pathologie du système nerveux central, et les femmes cessent de conduire plus tôt que les hommes. Au moment du diagnostic, 45% des hommes et 74% des femmes avaient cessé de conduire. Aucune différence de probabilité d'arrêt entre hommes et femmes ne subsistent 3 ans après le diagnostic. L'étude montre que peu de conducteurs déments conduisent après le diagnostic et ceux qui conduisent 3 ans après présentent tous une démence de type Alzheimer, dans laquelle les troubles des fonctions exécutives sont moins marqués que dans les autres types de démence. Même s'ils sont peu nombreux, il est important que les médecins accompagnent ces patients dans le processus d'arrêt de la conduite

: Lipids and incident dementia in men and women

International audienceCholesterol is a risk factor for developing vascular pathologies, which is in turn an important risk factor for dementia. Previous studies linking lipids and dementia have yielded inconsistent results, which may be attributable to sex differences in the etiology of both vascular disease and dementia. The aim of this study was to evaluate the associations between lipids and incident dementia in 7053 community-dwelling elderly. Dementia was diagnosed at baseline, and 2, 4, and 7-year follow-up. Multivariate Cox models stratified by sex and history of vascular pathologies at baseline were adjusted for sociodemographic, mental and physical health variables, and genetic vulnerability. In men without vascular pathologies, an increased incidence of all-cause dementia but not Alzheimer's disease (AD) was associated with high triglyceride (TG) (HR = 1.55, 95% CI = 1.04-2.32, p = 0.03) and low HDL-cholesterol levels (HR = 1.49, 95% CI = 0.99-2.23, p = 0.05). In women without vascular pathologies, low TG levels were associated with a decreased risk of AD (HR = 0.65, 95% CI = 0.43-0.97, p = 0.03). A decreased risk was also found with high TG levels which may depend on genetic vulnerability to dyslipidemia related to APOA5. For both sexes, no significant associations were found between total- or LDL-cholesterol and dementia or AD. Low HDL-cholesterol and high TG levels may be risk factors of dementia in elderly men whereas low TG is associated with decreased incident AD in women. This data suggests a complex sex-specific etiology of vascular dementia and AD

Lipid lowering agents, cognitive decline, and dementia: the three-city study.: Lipid Lowering Agents and Cognitive Decline

International audienceThe aim of this prospective cohort study was to evaluate the effects of lipid lowering agent (LLA) intake on cognitive function in 6,830 community-dwelling elderly persons. Cognitive performance (global cognitive functioning, visual memory, verbal fluency, psychomotor speed, and executive function), clinical diagnosis of dementia, and fibrate and statin use, were evaluated at baseline, and 2, 4, and 7 year follow-up. Multivariate Cox models were stratified by gender and adjusted for sociodemographic characteristics, mental and physical health including vascular risk factors, and genetic vulnerability (apolipoprotein E and cholesteryl ester transfer protein). For women but not men, fibrate use was specifically associated with an increased risk over 7 years of decline in visual memory only (HR = 1.29, 95% CI = 1.09-1.54, p = 0.004), and did not increase risk for incident dementia. This association was independent of genetic vulnerability related to apolipoprotein E and cholesteryl exchange transfer protein polymorphisms and occurred only in women with higher low density lipoprotein (LDL)-cholesterol levels and treated with fibrate (HR = 1.39, 95% CI = 1.08-1.79, p = 0.01) and not in those with lower LDL-cholesterol levels irrespective of fibrate treatment. For both genders, no significant associations were found between statins (irrespective of their lipophilicity) and either cognitive decline or dementia incidence. This prospective study, adjusting for multiple confounders, found no evidence that LLA given in late life reduced the risk of cognitive decline and dementia, but did raise the possibility that women with treatment-resistant high LDL-cholesterol may be at increased risk of decline in visual memory