Border management issues : border security and humanitarian aspects

"It has been predicted by the arts!" In 1990, the British screenwriter and novelist William Nicholson drew the attention to the mass movement of sub-Saharan citizens due to their bad living conditions in the film The March, a price winning BBC TV production. He described the migration of sub-Saharans to Europe, escaping from hunger and thirst. The initial small group is joined by more and more people on the march. Their dialogues inspire reflection. The leader of the group, Mahdi, argues as follows: “In Europe you have those wonderful small cats. We heard that one of these cats cost you more than 200 US Dollars a year. Let us be your cats. We could drink milk, lick your hands, we can purr and are much cheaper to be fed.”peer-reviewe

Knudsen gas provides nanobubble stability

We provide a model for the remarkable stability of surface nanobubbles to bulk dissolution. The key to the solution is that the gas in a nanobubble is of Knudsen type. This leads to the generation of a bulk liquid flow which effectively forces the diffusive gas to remain local. Our model predicts the presence of a vertical water jet immediately above a nanobubble, with an estimated speed of $\sim3.3\,\mathrm{m/s}$, in good agreement with our experimental atomic force microscopy measurement of $\sim2.7\,\mathrm{m/s}$. In addition, our model also predicts an upper bound for the size of nanobubbles, which is consistent with the available experimental data

The anatomy of a Volkspartei: the sociography of the membership of the NSDAP in Stadt- und Landkreis Wetzlar, 1925-1935

Der Beitrag analysiert anhand der Mitgliederlisten der NSDAP deren sozialstrukturelle Zusammensetzung in einer deutschen Kleinstadt mit vorwiegend protestantischer Bevölkerung. Im Zentrum der Auswertung und Interpretation stehen die Mitgliederzu- und abgänge der Partei während der 'Kampfzeit' bis 1933 und nach der 'Machtergreifung'. Die Daten zeigen anhand des sozialstrukturellen Merkmals 'Berufszugehörigkeit', daß es sich bei der NSDAP eindeutig um eine 'Volkspartei' gehandelt hat, d.h. ihre Rekrutierung und Mobilisierung verlief quer durch alle Schichten der Bevölkerung. Die Unterlagen über die Bewegungen im Mitgliederbestand und die schichtmäßige Zusammensetzung befinden sich heute im Hessischen Hauptstaatsarchiv Wiesbaden. (pre)'The analysis of the sociography of the NSDAP membership presented here is based on a complete set of data provided by a register of new members joining the party in Wetzlar town and county between 1930 and 1933, along with branch census returns drawn up in 1934 and 1935 relating to 46 of the 62 branches and cells established by the NSDAP in the region by 1933. These data permit not only a very detailed, comprehensive examination of the social contours of the membership mobilized by the NSDAP in a predominantly Protestant, rural and small-town milieu, but also throw light on the question as to which occupational groupings were involved in the relatively high membership turn-over which the party suffered from in its so-called Kampfzeit, an aspect of the Nazi Party about which we know little that is specific to date. The data show that the NSDAP mobilized a following in the Wetzlar region which transcended class divides, making the party a Volkspartei in social terms. In Wetzlar town and county the Nazi Party secured a membership whose occupational and class profile was astonishingly variable from branch to branch. The almost totally male, and predominantly young, membership was subjected to a high rate of membership turn-over in the early 1930s, in which the volatility among the working-class members drawn to the party before 1933 is particularly striking.' (author's abstract

Stabilization of free radical intermediates on metal oxide semiconductors surfaces

Free radicals intermediates are formed on the surface of metal oxide semiconductors, namely TiO_2 and Fe_2O_3, following the light-induced charge separation upon band-gap illumination. These radicals appear to adhere strongly to the surfaces of the small colloidal particles (diameters between 5 and 20 nm) employed in this study. A second electron-transfer step yielding the observed end-products therefore preceeds desorption of the reactive intermediates. Oxidation of methylviologen (1,1'-dimethyl-4,4'-bipyridylium chloride) and reduction of halothane (2-bromo-2-chloro-1,1,1- trifluoroethane) is thus found to proceed with high quantum yields and very specific mechanisms on colloidal TiO_2. The oxidation of sulfite on α-Fe_2O_3 particles yields the sulfite radical anion, SO_3^- , as initial intermediate. A subsequent electron transfer leading to the formation of sulfate occurs on the surface of the same catalyst particle

Mesoporous titania photocatalysts: Preparation, characterization and reaction mechanisms

Titanium dioxide is a very important semiconductor with a high potential for applications in photocatalysis, solar cells, photochromism, sensoring, and various other areas of nanotechnology. Increasing attention has recently been focused on the simultaneous achievement of high bulk crystallinity and the formation of ordered mesoporous TiO2 frameworks with high thermal stability. Mesoporous TiO2 has continued to be highly active in photocatalytic applications because it is beneficial for promoting the diffusion of reactants and products, as well as for enhancing the photocatalytic activity by facilitating access to the reactive sites on the surface of photocatalyst. This steady progress has demonstrated that mesoporous TiO2 nanoparticles are playing and will continue to play an important role in the protection of the environment and in the search for renewable and clean energy technologies. This review focuses on the preparation and characterisation of mesoporous titania, noble metals nanoparticles, transition metal ions, non-metal/doped mesoporous titania networks. The photocatalytic activity of mesoporous titania materials upon visible and UV illumination will be reviewed, summarized and discussed, in particular, concerning the influence of preparation and solid-state properties of the materials. Reaction mechanisms that are being discussed to explain these effects will be presented and critically evaluated. © The Royal Society of Chemistry 2011

Plasmonic Bubbles in n-Alkanes

In this paper we study the formation of microbubbles upon the irradiation of an array of plasmonic Au nanoparticles with a laser in n-alkanes ($C_{n}H_{2n+2}$, with n = 5-10). Two different phases in the evolution of the bubbles can be distinguished. In the first phase, which occurs after a delay time {\tau}d of about 100 {\mu}s, an explosive microbubble, reaching a diameter in the range from 10 {\mu}m to 100 {\mu}m, is formed. The exact size of this explosive microbubble barely depends on the carbon chain length of the alkane, but only on the laser power $P_l$. With increasing laser power, the delay time prior to bubble nucleation as well as the size of the microbubble both decrease. In the second phase, which sets in right after the collapse of the explosive microbubble, a new bubble forms and starts growing due to the vaporization of the surrounding liquid, which is highly gas rich. The final bubble size in this second phase strongly depends on the alkane chain length, namely it increases with decreasing number of carbon atoms. Our results have important implications for using plasmonic heating to control chemical reactions in organic solvents

One-step synthesis of mesoporous platinum/titania nanocomposites as photocatalyst with enhanced photocatalytic activity for methanol oxidation

Mesostructured Pt/TiO2 nanocomposites have been synthesized at different Pt (0–2 wt%) and anatase/rutile ratios through simple one-step sol–gel reactions. The as-made mesostructured hybrids were subjected to H2 gas for 2 h at 450 °C to obtain ordered hexagonal mesoporous Pt/TiO2 nanocomposites with highly crystalline TiO2. Subsequently, the samples were calcined at 350 °C in air for 4 h to remove the surfactant. XRD data clearly show that biphasial anatase and rutile mixtures are formed by the addition of the Pt islands. The TEM results indicated that TiO2 and Pt, are partly in close contact; the lattice fringes exhibit the typical distances, i.e., Pt (111) (2.2 Å) and TiO2 (101) (3.54 Å). TiO2 nanoparticles with an average diameter of about 10 nm particles are not agglomerated and quite uniform in size and shape. Also, Pt nanoparticles are well dispersed and exhibit diameters of about 5–12 nm based on the Pt content. Our photocatalysts have been compared with colloidal 0.5 wt% Pt loaded onto commercial photocatalysts either UV-100 Hombikat or Aeroxide TiO2 P25 by the determination of the initial rate of HCHO formation generated by the photooxidation of CH3OH in aqueous suspensions to calculate the corresponding photonic efficiencies. The overall photocatalytic activities of 0.5 wt% Pt/TiO2 nanocomposites are significantly 3-times higher than that of colloidal 0.5 wt% Pt loaded onto commercial photocatalysts either UV-100 Hombikat or Aeroxide TiO2 P25. To the best of our knowledge, the measured photonic efficiency ξ = 15.5% of hexagonal mesostructured Pt/TiO2 nanocomposites is found to be among the highest ξ values reported up to now. The superiority of Pt/TiO2 is attributed to the bicrystalline (anatase/rutile) framework, large surface area, high crystallinity and mesoporous structure of Pt/TiO2 nanocomposites

Universal mechanism for air entrainment during liquid impact

When a mm-sized liquid drop approaches a deep liquid pool, both the interface of the drop and the pool deform before the drop touches the pool. The build up of air pressure prior to coalescence is responsible for this deformation. Due to this deformation, air can be entrained at the bottom of the drop during the impact. We quantify the amount of entrained air numerically, using the Boundary Integral Method (BIM) for potential flow for the drop and the pool, coupled to viscous lubrication theory for the air film that has to be squeezed out during impact. We compare our results to various experimental data and find excellent agreement for the amount of air that is entrapped during impact onto a pool. Next, the impact of a rigid sphere onto a pool is numerically investigated and the air that is entrapped in this case also matches with available experimental data. In both cases of drop and sphere impact onto a pool the numerical air bubble volume V_b is found to be in agreement with the theoretical scaling V_b/V_{drop/sphere} ~ St^{-4/3}, where St is the Stokes number. This is the same scaling that has been found for drop impact onto a solid surface in previous research. This implies a universal mechanism for air entrainment for these different impact scenarios, which has been suggested in recent experimental work, but is now further elucidated with numerical results