Collective effects in light scattering from cold strontium clouds

A cold atomic cloud is a versatile object, because it offers many handles to control and tune its properties. This facilitates studies of its behavior in various circumstances, such as sample temperature, size and density, composition, dimensionality and coherence time. The range of possible experiments is constrained by the specifications of the atomic species used. In this thesis presents the work done in the experiment for laser cooling of strontium atoms, focusing on its stability, which should provide cold and ultracold samples for the study of collective effects in light scattering. From the initial apparatus, innumerous changes were performed. The vacuum system got improved and now reached lower ultra high vacuum due to the pre-baking done to its parts and adding a titanium-sublimation stage. The quadrupole trap were improved by the design and construction of a new pair of coils. The stability of the blue, green and red laser systems and the loss prevention of laser light were improved, giving rise to a robust apparatus. Another important point is the development of homemade devices to reduce the costs and to be used as a monitor of different parts of an cold atoms experiment. From this homemade devices, we could demonstrate a dramatic linewidth narrowing by injection lock of an low cost 461 nm diode laser and its application to our strontium experiment. In the end, this improved experimental apparatus made possible the study of a new scattering effect, the mirror assisted coherent back-scattering (mCBS).

New Middle East Cold War: Saudi Arabia and Iran's Rivalry

The competing powers of Saudi Arabia and Iran continue to redress and reverse the strategic imbalance and direction of the Middle East’s regional politics. The 1979 Iranian Revolution catapulted these two states into an embittered rivalry. The fall of Saddam Hussein following the 2003 U.S. led invasion, the establishment of a Shi’ite Iraq and the 2011 Arab Uprisings have further inflamed tensions between Saudi Arabia and Iran. Iran and Saudi Arabia have not confronted each other militarily, but rather have divided the region into two armed camps on the basis of political and religious ideology in seeking regional allies and promulgating sectarianism as they continue to exploit the region’s weak states in a series of proxy wars ranging from conflicts in Iraq to Lebanon. The Saudi-Iranian strategic and geopolitical rivalry is further complicated by a religious and ideological rivalry, as tensions represent two opposing aspirations for Islamic leadership with two vastly differing political systems. The conflict is between Saudi Arabia, representing Sunni Islam via Wahhabism, and Iran, representing Shi’ite Islam through Khomeinism. The nature of the Saudi-Iranian rivalry has led many Middle East experts to identify their rivalry as a “New Middle East Cold War.” The Saudi-Iranian rivalry has important implications for regional stability and U.S. national security interests. Therefore, this thesis seeks to address the question: Is a cold war framework applicable when analyzing the Saudi Arabian and Iranian relationship?

Abatement of hydrocarbons by acid ZSM-5 and BETA zeolites under cold-start conditions

Simulated cold-start tests have been carried out to evaluate the performance of H-ZSM-5 and H-BETA zeolites as hydrocarbon traps under simulated gasoline car exhaust gases, paying special attention to the effect of water on their behaviour. It is concluded that the hydrothermal treatment of the zeolites in the acidic form contributes to the better performance of these materials as hydrocarbon traps since the stabilization of the zeolites takes place. Moreover, the decrease of the surface acidity of the zeolites results in an increase of the Si/Al ratio, which contributes to the decrease of the water affinity for adsorption sites. Thus, the competition with hydrocarbon molecules in the exhaust for the adsorption sites is reduced which increases their trap efficiency. The stabilized H-ZSM-5 is the zeolite that showed the best performance with a propene offset temperature of 240 °C, which should be high enough for the three-way catalyst to carry out its role as catalytic converter.

CuH-ZSM-5 as Hydrocarbon Trap under Cold Start Conditions

Cold start tests are carried out to evaluate the performance of copper-exchanged zeolites as hydrocarbon traps under simulated gasoline car exhaust gases, paying special attention to the role of copper in the performance of these zeolites. It is concluded that the partial substitution of the protons in the parent H-ZSM-5 zeolite is highly beneficial for hydrocarbon trapping due to the formation of selective adsorption sites with specific affinity for the different exhaust components. However, it is also observed that uncontrolled exchanging process conditions could lead to the presence of CuO nanoparticles in the zeolite surface, which seem to block the pore structure of the zeolite, decreasing the hydrocarbon trap efficiency. Among all the zeolites studied, the results point out that a CuH-ZSM-5 with a partial substitution of extra-framework protons by copper cations and without any detectable surface CuO nanoparticles is the zeolite that showed the best performance under simulated cold start conditions due to both the high stability and the hydrocarbon retaining capacity of this sample during the consecutive cycles.

BETA Zeolite Thin Films Supported on Honeycomb Monoliths with Tunable Properties as Hydrocarbon Traps under Cold-Start Conditions

A high percentage of hydrocarbon (HC) emissions from gasoline vehicles occur during the cold-start period. Among the alternatives proposed to reduce these HC emissions, the use of zeolites before the three-way catalyst (TWC) is thought to be very effective. Zeolites are the preferred adsorbents for this application; however, to avoid high pressure drops, supported zeolites are needed. In this work, two coating methods (dip-coating and in situ crystallization) are optimized to prepare BETA zeolite thin films supported on honeycomb monoliths with tunable properties. The important effect of the density of the thin film in the final performance as a HC trap is demonstrated. A highly effective HC trap is prepared showing 100 % toluene retention, accomplishing the desired performance as a HC trap, desorbing propene at temperatures close to 300 °C, and remaining stable after cycling. The use of this material before the TWC is very promising, and works towards achieving the sustainability and environmental protection goals.

Optimizing the performance of catalytic traps for hydrocarbon abatement during the cold-start of a gasoline engine

A key target to reduce current hydrocarbon emissions from vehicular exhaust is to improve their abatement under cold-start conditions. Herein, we demonstrate the potential of factorial analysis to design a highly efficient catalytic trap. The impact of the synthesis conditions on the preparation of copper-loaded ZSM-5 is clearly revealed by XRD, N2 sorption, FTIR, NH3-TPD, SEM and TEM. A high concentration of copper nitrate precursor in the synthesis improves the removal of hydrocarbons, providing both strong adsorption sites for hydrocarbon retention at low temperature and copper oxide nanoparticles for full hydrocarbon catalytic combustion at high temperature. The use of copper acetate precursor leads to a more homogeneous dispersion of copper oxide nanoparticles also providing enough catalytic sites for the total oxidation of hydrocarbons released from the adsorption sites, although lower copper loadings are achieved. Thus, synthesis conditions leading to high copper loadings jointly with highly dispersed copper oxide nanoparticles would result in an exceptional catalytic trap able to reach superior hydrocarbon abatement under highly demanding operational conditions.

Battle of Cold Harbor, Virginia and vicinity, 1864 (Raster Image)

This layer is a georeferenced raster image of the untitled historic paper manuscript map: [Map of the Battle of Cold Harbor, Virginia and vicinity]. Scale not given. Covers a portion of Hanover County, Virginia, showing features in the region surrounding the Cold Harbor Battlefield, Virginia, 1864. The image inside the map neatline is georeferenced to the surface of the earth and fit to the Virginia State Plane South Coordinate System (in Meters) (Fipszone 4502). All map collar and inset information is also available as part of the raster image, including any inset maps, profiles, statistical tables, directories, text, illustrations, or other information associated with the principal map. This map shows features such as roads, towns and villages, drainage, dwellings with names of inhabitants, troop locations with dates, and more. This layer is part of a selection of digitally scanned and georeferenced historic maps of the Civil War from the Harvard Map Collection. Many items from this selection are from a collection of maps deposited by the Military Order of the Loyal Legion of the United States Commandery of the State of Massachusetts (MOLLUS) in the Harvard Map Collection in 1938. These maps typically portray both natural and manmade features, in particular showing places of military importance. The selection represents a range of regions, originators, ground condition dates, scales, and purposes.

The differential evolution of hot- and cold-dust in galaxies in the last 7.5 GYR

Tese de mestrado em Física, apresentada à Universidade de Lisboa, através da Faculdade de Ciências, 2016

Too cold to handle: EU accession talks with Iceland. CEPS Commentary, 3 June 2013

Recent opinion polls suggest that most Icelanders are against joining the EU. By the same token, however, a majority of those polled are in favour of continuing accession talks. These results show that Iceland’s relationship with the EU is a deeply divisive issue within the country. Although no date for the referendum has been set, the new centre-right coalition may thus want to settle this matter as soon as possible. Should there indeed be a majority in support of continuing negotiations, then Iceland’s accession process will become a complicated and cool affair in the hands of an anti-EU membership coalition government.

Will Crimea herald a new post-Cold War era world? EPC Commentary, 7 April 2014

The end of the Cold War twenty-five years ago brought about a difficult but manageable world in which Russia, the US, and European countries cooperated to manage common problems. There have been difficult times, with the break up of former Yugoslavia, the NATO intervention for Kosovo, and in 2008 when Russia’s intervention in Georgia’s breakaway regions of South Ossetia and Abkahzia nearly led to a head to head with the West. On the whole, the cooperation between old foes which framed the end of the Cold War, resisted these tests. The Helsinki Final Act of 1975 and the agreement not to redraw the map of Europe was never so evidently ignored as today.