A perspective of synthetic aperture radar for remote sensing

The characteristics and capabilities of synthetic aperture radar are discussed so as to identify those features particularly unique to SAR. The SAR and Optical images were compared. The SAR is an example of radar that provides more information about a target than simply its location. It is the spatial resolution and imaging capability of SAR that has made its application of interest, especially from spaceborne platforms. However, for maximum utility to remote sensing, it was proposed that other information be extracted from SAR data, such as the cross section with frequency and polarization

The Paradox of Unemployment and Job Vacancies : Some Theories Confronted by Data

Les causes principales du paradoxe résultant de la simultanéité du chômage et de la disponibilité d'emplois sont les suivantes: les changements subits du niveau et des composantes de l'activité économique, l'imperfection des voies d'accès aux marchés du travail, la répugnance des employeurs et des planificateurs sociaux à considérer le travail comme une ressource à développer et à planifier à long terme plutôt qu'à le traiter « comme un robinet qu'on ouvre et qu'on ferme à discrétion suivant les conditions économiques immédiates ».Une des conséquences de cette dernière attitude fut que le « pipe-line » de la main-d'oeuvre s'est en réalité rompu au cours de la période de faible croissance qui a marqué les années 1967 à 1972. « Une fois ainsi brisé, il devenait impossible de le remettre en état au moment de l'expansion soudaine qui a commencé en 1973 ».L'article souligne que l'assurance-chômage favorise quelque peu le paradoxe précédent, mais que la presse a vraiment amplifié son importance. Les attaques contre le régime d'assurance-chômage visaient surtout à détourner l'attention des véritables problèmes.Les chercheurs n'ont découvert aucune confirmation statistique qu'une proportion accrue des gens conseillés par les centres de main-d'oeuvre du Canada aux employeurs éventuels ne s'y rendaient que pour la forme en vue de conserver leurs droits aux prestations. La confirmation de ce fait aurait été de nature à affermir la prétention que l'assurance-chômage favorisait le chômage de personnes qui ne veulent pas travailler.Parmi les personnes qui avaient été recommandées aux employeurs, il ne s'en trouvait qu'un très petit nombre dans le premier quart de 1974 qui refusaient des emplois, alors que le chômage s'accroissait et que les réclamations étaient attentivement scrutées.Toutefois, les chercheurs ont découvert des signes d'une augmentation considérable du taux des rejets de la part des employeurs. En effet, entre 1969 et la première moitié de 1974, le pourcentage des candidats embauchés est tombé de 45.2 à 29.3.Aussi, conclure que la plupart des travailleurs alors en chômage n'étaient pas considérés comme acceptables, comme beaucoup le prétendent, traduit un état quasi désespéré de postes vacants.En d'autres mots, le marché du travail était déséquilibré structurellement. Les caractéristiques de la main-d'oeuvre (âge, sexe, qualification, formation, métier, expérience, perfectionnement, lieu de résidence) ne correspondaient pas aux besoins des employeurs.Au sujet de la qualification, par exemple, on observait de fortes hausses dans la disponibilité des emplois, mais peu ou pas d'accroissement des embauchages dans les postes administratifs, les sciences naturelles, le génie, les mathématiques, la médecine et les autres sciences de la santé. Par contre, il y avait diminution des emplois vacants dans le cas des commis-vendeurs où les embauchages furent considérables.Le taux de chômage était continuellement plus haut chez les femmes que chez les hommes, chez les jeunes que chez les adultes. Le groupe d'âge de moins de 21 ans comptait pour 32 pour cent de l'ensemble des sans-travail au milieu de 1974, mais il ne représentait que 13 pour cent des réclamants.La raison en était qu'une forte proportion des jeunes chômeurs n'avaient pas encore réussi à obtenir un premier emploi et qu'ils n'étaient pas admissibles aux prestations d'assurance-chômage.Ce qui en ressort, c'est que l'assurance-chômage n'a guère de signification lorsqu'il s'agit pour elle d'aider ceux pour qui le chômage est un problème aigu. Ceci contredit le reproche que l'on fait aux jeunes de tirer profit du régime d'assurance-chômage.L'immigration peut aider à résoudre les postes vacants dans certains cas particuliers, mais elle ne saurait y répondre d'une façon globale. Y croire équivaudrait à perpétuer l'approche actuelle qui consiste à ouvrir et à fermer le robinet au besoin, source principale des problèmes actuels en matière de main-d'oeuvre.Ce qui importe le plus, c'est améliorer les façons d'utiliser les ressources humaines, en particulier, les jeunes, les femmes et les groupes minoritaires. Il nous faut beaucoup plus pour leur faciliter la découverte d'emplois qui les satisfassent. Tout ce qui faciliterait tant pour les maisons d'enseignement que pour les employeurs un budget de fonctionnement à plus long terme ferait disparaître un des obstacles majeures à la planification de la main-d'oeuvre. Il suffirait d'un peu plus d'imagination pour remplacer par quelque formule originale, surtout pour les jeunes, la formation en usine et l'expérience acquise.Postes vacants et chômage élevé peuvent coexister, mais l'assurance-chômage n'est pas la raison principale de ce paradoxe.The purpose of this paper is to see just how well available data enable us to come to grips with the apparent paradox of simultaneous job vacancies and unemployment

Conveyor belt clock synchronization

A protocol for synchronizing distant clocks is proposed that does not rely on the arrival times of the signals which are exchanged, and an optical implementation based on coherent-state pulses is described. This protocol is not limited by any dispersion that may be present in the propagation medium through which the light signals are exchanged. Possible improvements deriving from the use of quantum-mechanical effects are also addressed.Comment: 8 pages, 7 figure

Magnetic-field-induced singularities in spin dependent tunneling through InAs quantum dots

Current steps attributed to resonant tunneling through individual InAs quantum dots embedded in a GaAs-AlAs-GaAs tunneling device are investigated experimentally in magnetic fields up to 28 T. The steps evolve into strongly enhanced current peaks in high fields. This can be understood as a field-induced Fermi-edge singularity due to the Coulomb interaction between the tunneling electron on the quantum dot and the partly spin polarized Fermi sea in the Landau quantized three-dimensional emitter.Comment: 5 pages, 4 figure

Political Mediation and American Old-Age Security Exceptionalism

Debates over America’s heavy reliance on employer-provided private pensions have understated the profound role organized labor played after World War II. Archival evidence from prominent unions and business associations suggests that the shift in organized labor’s strategy after the New Deal toward electoral activity helps explain critical interventions by Northern Democrats into the system of private pensioning in the postwar period that laid the foundation for America’s old-age security system. Such a strategy was insufficient, however, to expand Social Security. This article offers a political mediation account of electoral activity as a source of labor influence on social policy that draws on political institutionalist and class power theories

Using polarized maser to detect high-frequency relic gravitational waves

A GHz maser beam with Gaussian-type distribution passing through a homogenous static magnetic field can be used to detect gravitational waves (GWs) with the same frequency. The presence of GWs will perturb the electromagnetic (EM) fields, giving rise to perturbed photon fluxes (PPFs). After being reflected by a fractal membrane, the perturbed photons suffer little decay and can be measured by a microwave receiver. This idea has been explored to certain extent as a method for very high frequency gravitational waves. In this paper, we examine and develop this method more extensively, and confront the possible detection with the predicted signal of relic gravitational waves (RGWs). A maser beam with high linear polarization is used to reduce the background photon fluxes (BPFs) in the detecting direction as the main noise. As a key factor of applicability of this method, we give a preliminary estimation of the sensitivity of a sample detector limited by thermal noise using currently common technology. The minimal detectable amplitude of GWs is found to be $h_{\rm{min}}\sim10^{-30}$. Comparing with the known spectrum of the RGWs in the accelerating universe for $\beta=-1.9$, there is still roughly a gap of $4\sim 5$ orders. However, possible improvements on the detector can further narrow down the gap and make it a feasible method to detect high frequency RGWs.Comment: 20 pages, 6 figures, accepted for Phys. Rev.

A polarimetric Doppler radar time‐series simulator for biological applications

The high mobility of airborne organisms makes them inherently difficult to study, motivating the use of radars and radar networks as biological surveillance tools. While the utility of radar for ecological studies has been demonstrated, a number of challenges remain in expanding and optimizing their use for surveillance of birds, bats and insects. To explore these topics, a Lagrangian simulation scheme has been developed to synthesize realistic, polarimetric, pulsed Doppler radar baseband signals from modelled flocks of biological point scatterers. This radar simulation algorithm is described, and an application is presented using an agent-based model of the nocturnal emergence of a cave-dwelling colony of Brazilian free-tailed bats (Tadarida brasiliensis). Dualpolarization radar signals for an S-band weather surveillance radar are synthesized and used to develop a new extension of the spectral velocity azimuth display for polarimetric roost-ring signature analysis, demonstrating one capability of this simulation scheme. While these developments will have direct benefits for radar engineers and meteorologists, continuing investment in radar methods such as these will have cascading effects toward improving ecological models and developing new observational techniques for monitoring aerial wildlife

Acceptability of HIV self-sampling kits (TINY vial) among people of black African ethnicity in the UK: a qualitative study

Background: Increasing routine HIV testing among key populations is a public health imperative, so improving access to acceptable testing options for those in need is a priority. Despite increasing targeted distribution and uptake of HIV self-sampling kits (SSKs) among men who have sex with men in the UK, little is known about why targeted SSK interventions for black African users are not as wide-spread or well-used. This paper addresses this key gap, offering insight into why some groups may be less likely than others to adopt certain types of SSK interventions in particular contexts. These data were collected during the development phase of a larger study to explore the feasibility and acceptability of targeted distribution of SSKs to black African people. Methods: We undertook 6 focus groups with members of the public who self-identified as black African (n = 48), 6 groups with specialists providing HIV and social services to black African people (n = 53), and interviews with HIV specialist consultants and policy-makers (n = 9). Framework analysis was undertaken, using inductive and deductive analysis to develop and check themes. Results: We found three valuable components of targeted SSK interventions for this population: the use of settings and technologies that increase choice and autonomy; targeted offers of HIV testing that preserve privacy and do not exacerbate HIV stigma; and ensuring that the specific kit being used (in this case, the TINY vial) is perceived as simple and reliable. Conclusions: This unique and rigorous research offers insights into participants’ views on SSK interventions, offering key considerations when targeting this population.. Given the plethora of HIV testing options, our work demonstrates that those commissioning and delivering SSK interventions will need to clarify (for users and providers) how each kit type and intervention design adds value. Most significantly, these findings demonstrate that without a strong locus of control over their own circumstances and personal information, black African people are less likely to feel that they can pursue an HIV test that is safe and secure. Thus, where profound social inequalities persist, so will inequalities in HIV testing uptake – by any means

Quantitative analysis of lab-to-lab variability in Caco-2 permeability assays

In this study, Caco-2 permeability results from different laboratories were compared. Six different sets of apparent permeability coefficient (Papp) values reported in the literature were compared to experimental Papp obtained in our laboratory. The differences were assessed by determining the root mean square error (RMSE) values between the datasets, which reached levels as high as 0.581 for the training set compounds, i.e. ten compounds with known effective human permeability (Peff). The consequences of these differences in Papp for prediction of oral drug absorption were demonstrated by introducing the Papp into the absorption and pharmacokinetics simulation software application GastroPlus™ for prediction of the fraction absorbed (Fa) in humans using calibrated “user-defined permeability models”. The RMSE were calculated to assess the differences between the simulated Fa and experimental values reported in the literature. The RMSE for Fa simulated with the permeability model calibrated using experimental Papp from our laboratory was 0.128. When the calibration was performed using Papp from literature datasets, the RMSE values for Fa were higher in all cases except one. This study shows quantitative lab-to-lab variability of Caco-2 permeability results and the potential consequences this can have in the use of these results for predicting intestinal absorption of drugs