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

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

Transverse energy production and charged-particle multiplicity at midrapidity in various systems from sNN=7.7\sqrt{s_{NN}}=7.7 to 200 GeV

Measurements of midrapidity charged particle multiplicity distributions, $dN_{\rm ch}/d\eta$, and midrapidity transverse-energy distributions, $dE_T/d\eta$, are presented for a variety of collision systems and energies. Included are distributions for Au$+$Au collisions at $\sqrt{s_{_{NN}}}=200$, 130, 62.4, 39, 27, 19.6, 14.5, and 7.7 GeV, Cu$+$Cu collisions at $\sqrt{s_{_{NN}}}=200$ and 62.4 GeV, Cu$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV, U$+$U collisions at $\sqrt{s_{_{NN}}}=193$ GeV, $d$$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV, $^{3}$He$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV, and $p$$+$$p$ collisions at $\sqrt{s_{_{NN}}}=200$ GeV. Centrality-dependent distributions at midrapidity are presented in terms of the number of nucleon participants, $N_{\rm part}$, and the number of constituent quark participants, $N_{q{\rm p}}$. For all $A$$+$$A$ collisions down to $\sqrt{s_{_{NN}}}=7.7$ GeV, it is observed that the midrapidity data are better described by scaling with $N_{q{\rm p}}$ than scaling with $N_{\rm part}$. Also presented are estimates of the Bjorken energy density, $\varepsilon_{\rm BJ}$, and the ratio of $dE_T/d\eta$ to $dN_{\rm ch}/d\eta$, the latter of which is seen to be constant as a function of centrality for all systems.Comment: 706 authors, 32 pages, 20 figures, 34 tables, 2004, 2005, 2008, 2010, 2011, and 2012 data. v2 is version accepted for publication in Phys. Rev.

Nuclear matter effects on J/ψJ/\psi production in asymmetric Cu+Au collisions at sNN\sqrt{s_{_{NN}}} = 200 GeV

We report on $J/\psi$ production from asymmetric Cu+Au heavy-ion collisions at $\sqrt{s_{_{NN}}}$=200 GeV at the Relativistic Heavy Ion Collider at both forward (Cu-going direction) and backward (Au-going direction) rapidities. The nuclear modification of $J/\psi$ yields in Cu$+$Au collisions in the Au-going direction is found to be comparable to that in Au$+$Au collisions when plotted as a function of the number of participating nucleons. In the Cu-going direction, $J/\psi$ production shows a stronger suppression. This difference is comparable in magnitude and has the same sign as the difference expected from shadowing effects due to stronger low-$x$ gluon suppression in the larger Au nucleus. The relative suppression is opposite to that expected from hot nuclear matter dissociation, since a higher energy density is expected in the Au-going direction.Comment: 349 authors, 10 pages, 4 figures, and 4 tables. Submitted to Phys. Rev. C. For v2, fixed LaTeX error in 3rd-to-last sentence. Plain text data tables for the points plotted in figures for this and previous PHENIX publications are (or will be) publicly available at http://www.phenix.bnl.gov/papers.htm

Inclusive cross section and double-helicity asymmetry for π0\pi^{0} production at midrapidity in pp++pp collisions at s=510\sqrt{s}=510 GeV

PHENIX measurements are presented for the cross section and double-helicity asymmetry ($A_{LL}$) in inclusive $\pi^0$ production at midrapidity from $p$$+$$p$ collisions at $\sqrt{s}=510$~GeV from data taken in 2012 and 2013 at the Relativistic Heavy Ion Collider. The next-to-leading-order perturbative-quantum-chromodynamics theory calculation is in excellent agreement with the presented cross section results. The calculation utilized parton-to-pion fragmentation functions from the recent DSS14 global analysis, which prefer a smaller gluon-to-pion fragmentation function. The $\pi^{0}A_{LL}$ results follow an increasingly positive asymmetry trend with $p_T$ and $\sqrt{s}$ with respect to the predictions and are in excellent agreement with the latest global analysis results. This analysis incorporated earlier results on $\pi^0$ and jet $A_{LL}$, and suggested a positive contribution of gluon polarization to the spin of the proton $\Delta G$ for the gluon momentum fraction range $x>0.05$. The data presented here extend to a currently unexplored region, down to $x\sim0.01$, and thus provide additional constraints on the value of $\Delta G$. The results confirm the evidence for nonzero $\Delta G$ using a different production channel in a complementary kinematic region.Comment: 413 authors, 8 pages, 4 figures. v2 is version accepted as PRD Rapid Communication. Plain text data tables for the points plotted in figures for this and previous PHENIX publications are (or will be) publicly available at http://www.phenix.bnl.gov/papers.htm

Single electron yields from semileptonic charm and bottom hadron decays in Au++Au collisions at sNN=200\sqrt{s_{NN}}=200 GeV

The PHENIX Collaboration at the Relativistic Heavy Ion Collider has measured open heavy-flavor production in minimum bias Au$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV via the yields of electrons from semileptonic decays of charm and bottom hadrons. Previous heavy-flavor electron measurements indicated substantial modification in the momentum distribution of the parent heavy quarks due to the quark-gluon plasma created in these collisions. For the first time, using the PHENIX silicon vertex detector to measure precision displaced tracking, the relative contributions from charm and bottom hadrons to these electrons as a function of transverse momentum are measured in Au$+$Au collisions. We compare the fraction of electrons from bottom hadrons to previously published results extracted from electron-hadron correlations in $p$$+$$p$ collisions at $\sqrt{s_{_{NN}}}=200$ GeV and find the fractions to be similar within the large uncertainties on both measurements for $p_T>4$ GeV/$c$. We use the bottom electron fractions in Au$+$Au and $p$$+$$p$ along with the previously measured heavy flavor electron $R_{AA}$ to calculate the $R_{AA}$ for electrons from charm and bottom hadron decays separately. We find that electrons from bottom hadron decays are less suppressed than those from charm for the region $3<p_T<4$ GeV/$c$.Comment: 432 authors, 33 pages, 23 figures, 2 tables, 2011 data. v2 is version accepted for publication by Phys. Rev. C. Plain text data tables for the points plotted in figures for this and previous PHENIX publications are (or will be) publicly available at http://www.phenix.bnl.gov/papers.htm