Arctic Sea Ice Microstructure Observations Relevant to Microwave Scattering

Sea ice microstructure characteristics relevant to ice microwave scattering were studied during SIMMS'91 field experiment in Resolute Bay in May/June 1991. Thin sections of the top 300 mm layer of first-year ice (from hummocks and melt ponds) were prepared and examined. Analysis is based mostly on qualitative observations, although statistics on bubble dimensions and geometry were obtained from digital analysis of thin section photographs. First-year ice featured mostly an oriented columnar grain structure. Both spherical and needle-shaped brine pockets were observed. In multi-year ice, a variety of grain structures and inclusion patterns were observed from the same floe. Hummock and melt pond ice are different in terms of grain structure and air bubble contents. Air bubbles in hummock ice are highly random and interconnected, especially near the surface. At lower depths, they retain simpler shapes and become oriented parallel to the dominant grain growth direction. In melt pond ice, two types of air inclusions whose typical dimensions differ by an order of magnitude were observed. Significant spatial variability of multi-year microstructure within a single floe is demonstrated.Key words: sea ice, ice microstructure, ice microwave scattering, SAR ice signatures, air bubbles in sea iceAu cours de l'étude de terrain SIMMS'91 menée dans la baie Resolute en mai/juin 1991, on a étudié les caractéristiques de la microstructure de la glace de mer pertinentes à la diffusion d'hyperfréquences par la glace. On a préparé et examiné de fines coupes transversales prélevées dans les 300 mm supérieurs de la glace de l'année et de la glace pluri-annuelle (provenant de hummocks et de mares de fonte). L'analyse s'appuie principalement sur des observations qualitatives, bien que les statistiques sur les dimensions et la géométrie des bulles aient été obtenues à partir du traitement numérique de photographies représentant de fines coupes transversales. La glace de l'année affichait principalement une structure granulaire prismée. On a observé des poches de saumure sphériques ainsi qu'aciculaires. Dans la glace pluri-annuelle, on a observé dans le même floe une diversité de structures granulaires et de schémas d'inclusion. Les hummocks et la glace des mares de fonte diffèrent quant à leur structure granulaire et au contenu des bulles d'air. Dans la glace de hummock, les bulles d'air sont distribuées au hasard et reliées entre elles, surtout près de la surface. À de plus grandes profondeurs, elles conservent des formes plus simples et s'orientent parallèlement à la direction dominante de la croissance granulaire. Dans la glace des mares de fonte, on retrouve deux types d'inclusions d'air dont les dimensions typiques diffèrent d'un ordre de grandeur. On démontre qu'il existe une importante variabilité spatiale de la microstructure de la glace pluri-annuelle à l'intérieur d'un même floe.Mots clés: glace de mer, microstructure de la glace, diffusion d’hyperfréquences par la glace, signatures de la glace obtenues avec le RALS, bulles d’air dans la glace de me

A Moment Method for the Second Order Two-point Boundary Value Problems

In this paper a Moment method based on the second, third and fourth kindChebyshev polynomials is proposed to approximate the solution of a linear twopointboundary value problem of the second order. The proposed method isflexible, easy to program and efficient. Two numerical examples are given forconciliating the results of this method, all the computation results are obtainedusing Matlab

Performing the Egyptian revolution : origins of collective restraint action in the Midan

This research was supported by a Carnegie Trust for the Universities of Scotland grant.In January/February 2011, the world watched with admiration the Egyptian revolution that toppled President Housni Mubarak. The demonstration in Midan al-Tahrir (Liberation Square in central Cairo), which was the nucleus of the revolution, highlighted a largely spontaneous, civil and peaceful political performance. However, this performance was temporary, contradicting subsequent bloody conflicts in post-revolutionary Egypt. This article examines the socio-political origins of the Midan performance. It argues that the demonstrators exercised collective restraint, which was temporary but necessary, in order to topple Mubarak. Building on Norbert Elias’ civilising process theory and social movements literature, it is argued that the origins of this performance are found in a collective knowledge of regime strategy and narrative, Egyptian socio-political values and existing repertoires of contention. Drawing on primary sources and semi-structured interviews, the article contends that the demonstrators exercised collective restraint to reframe regime narrative and draw public support for the revolution.PostprintPeer reviewe

Field Validation of ERS-1 SAR Images of Sea Ice in Resolute Region

NRC publication: Ye

Modeling of charged-particle multiplicity and transverse-momentum distributions in pp collisions using a DNN

A machine learning technique is used to fit multiplicity distributions in high energy proton-proton collisions and applied to make predictions for collisions at higher energies. The method is tested with Monte Carlo event generators. Charged-particle multiplicity and transverse-momentum distributions within different pseudorapidity intervals in proton-proton collisions were simulated using the PYTHIA event generator for center of mass energies $\sqrt{s}$= 0.9, 2.36, 2.76, 5, 7, 8, 13 TeV for model training and validation and at 10, 20, 27, 50, 100 and 150 TeV for model predictions. Comparisons are made in order to ensure the model reproduces the relation between input variables and output distributions for the charged particle multiplicity and transverse-momentum. The multiplicity and transverse-momentum distributions are described and predicted very well, not only in the case of the trained but also in the case of untrained energy values. The study proposes a way to predict multiplicity distributions at a new energy by extrapolating the information inherent in the lower energy data. Using real data instead of Monte Carlo, as measured at the LHC, the technique has the potential to project the multiplicity distributions for different intervals at very high collision energies, e.g. 27 TeV or 100 TeV for the upgraded HE-LHC and FCC-hh respectively, using only data collected at the LHC, i.e. at center of mass energies from 0.9 up to 13 TeV.A machine learning technique is used to fit multiplicity distributions in high-energy proton-proton collisions and applied to make predictions for collisions at higher energies. The method is tested with Monte Carlo event generator events. Charged-particle multiplicity and transverse-momentum distributions within different pseudorapidity intervals in proton-proton collisions were simulated using the PYTHIA event generator for center of mass energies $\sqrt{s}$= 0.9, 2.36, 2.76, 5, 7, 8, 13 TeV for model training and validation and at 10, 20, 27, 50, 100 and 150 TeV for model predictions. Comparisons are made in order to ensure the model reproduces the relation input variables and output distributions for the charged particle multiplicity and transverse-momentum. The multiplicity and transverse-momentum distributions are described and predicted very well, not only in the case of the trained but also in the untrained energy values. The study proposes a way to predict multiplicity distributions at a new energy by extrapolating the information inherent in the lower energy data. Using real data instead of Monte Carlo, as measured at the LHC, the technique has the potential to project the multiplicity distributions for different intervals at very high collision energies, e.g. 27 TeV or 100 TeV for the upgraded HE-LHC and FCC-hh respectively, using only data collected at the LHC, i.e. at center of mass energies from 0.9 up to 13 TeV

Field Validation of ERS-1 SAR Images of Sea Ice in Resolute Region

NRC publication: Ye

Study of charged-particle multiplicity fluctuations in pp collisions with Monte Carlo event generators at the LHC

Proton-Proton ($pp$) collisions at the Large Hadron Collider (LHC) are simulated in order to study events with a high local density of charged particles produced in narrow pseudorapidty windows of $\Delta\eta$ = 0.1, 0.2, and 0.5. The $pp$ collisions are generated at center of mass energies of $\sqrt{s} = 2.36$, $7$, $8$, and $13$ TeV, i.e. the energies at which the LHC has operated so far, using PYTHIA and HERWIG event generators. We have also studied the average of the maximum charged-particle density versus the event multiplicity for all events, using the different pseudorapidity windows. This study prepares for the multi-particle production background expected in a future search for anomalous high-density multiplicity fluctuations using the LHC data.Proton–Proton (pp) collisions at the Large Hadron Collider (LHC) are simulated in order to study events with a high local density of charged particles produced in narrow pseudorapidty windows of Δη = 0.1, 0.2, and 0.5. The pp collisions are generated at center of mass energies of s = 2.36, 7, 8, and 13 TeV, i.e., the energies at which the LHC has operated so far, using PYTHIA and HERWIG event generators. We have also studied the average of the maximum charged-particle density versus the event multiplicity for all events, using the different pseudorapidity windows. This study prepares for the multi-particle production background expected in a future search for anomalous high-density multiplicity fluctuations using the LHC data