Advanced undergraduate experiments in vacuum physics and mass spectrometry

A comprehensive high‐vacuum system has been set up and operated in an advanced undergraduate laboratory for students majoring in physics and microelectronics. The aim of the experiment is to provide the students with both practical experience and basic theoretical understanding of the production and measurement of low pressures. The students measure the pumping speed of a rotary forepump and of an oil diffusion pump, as a function of pressure, using procedures adopted by the AVS. A hot‐cathode ionization gauge and a thermocouple gauge are calibrated against a McLeod (absolute) manometer for several gases. The compositions of ambient air, of an isotopic mixture of neon, and of the residual gases in an oil‐diffusion‐pumped system are determined with the aid of a mass spectrometer. The influence of a liquid‐nitrogen‐cooled surface is assessed. Helium leak detection is demonstrated, and the response and sensitivity of the mass spectrometer as a leak detector are evaluated

Pulsed electron beam induced recrystallization and damage in GaAs

Single-pulse electron-beam irradiations of 300-keV 10^(15)Kr+/cm^2 or 300-keV 3×10^(12)Se+/cm^2 implanted layers in unencapsulated GaAs are studied as a function of the electron beam fluence. The electron beam pulse had a mean electron energy of ~-20 keV and a time duration of ~-10^(–7) s. Analyses by means of MeV He + channeling and TEM show the existence of narrow fluence window (0.4–0.7 J/cm^2) within which amorphous layers can be sucessfully recrystallized, presumably in the liquid phase regime. Too high a fluence produces extensive deep damage and loss of As

Steady-state thermally annealed GaAs with room-temperature-implanted Si

Semi-insulating Cr-doped single-crystal GaAs samples were implanted at room temperature with 300-keV Si ions in the dose range of (0.17–2.0)×1015 cm–2 and were subsequently steady-state annealed at 900 and 950°C for 30 min in a H2 ambient with a Si3N4 coating. Differential Hall measurements showed that an upper threshold of about 2×1018/cm3 exists for the free-electron concentration. The as-implanted atomic-Si profile measured by SIMS follows the theoretical prediction, but is altered during annealing. The Cr distribution also changes, and a band of dislocation loops ~2–3 kÅ wide is revealed by cross-sectional TEM at a mean depth of Rp~3 kÅ. Incomplete electrical activation of the Si is shown to be the primary cause for the effect

The thickness of a liquid layer on the free surface of ice as obtained from computer simulation

Molecular dynamic simulations were performed for ice Ih with a free surface by using four water models, SPC/E, TIP4P, TIP4P/Ice and TIP4P/2005. The behavior of the basal plane, the primary prismatic plane and of the secondary prismatic plane when exposed to vacuum was analyzed. We observe the formation of a thin liquid layer at the ice surface at temperatures below the melting point for all models and the three planes considered. For a given plane it was found that the thickness of a liquid layer was similar for different water models, when the comparison is made at the same undercooling with respect to the melting point of the model. The liquid layer thickness is found to increase with temperature. For a fixed temperature it was found that the thickness of the liquid layer decreases in the following order: the basal plane, the primary prismatic plane, and the secondary prismatic plane. For the TIP4P/Ice model, a model reproducing the experimental value of the melting temperature of ice, the first clear indication of the formation of a liquid layer appears at about -100 Celsius for the basal plane, at about -80 Celsius for the primary prismatic plane and at about -70 Celsius for the secondary prismatic plane.Comment: 41 pages and 13 figure

Cyberspace as a Precondition of the application of law in a multicentric European legal area

Cyberspace as a Precondition of the application of law in a multicentric European legal are

Intencjonalność i intersubiektywność a zasada kauzalności w polskim prawie cywilnym

The paper presents and discusses the principle of causability as expressed in many civil codes. This principle requires that the existence of any obligations of transfers of ownership the legal cause – usually associated with 3 types of dealings having been identified by Roman jurists and elaborated by postglosators and founders of the 17th-century natural law movement, namely: causa solvendi, donandi, aquirendi, or causa cavendi – creates a condition for validity of legal act. Referring to the philosophical background of the analytical philosophy of intention and intersubjectivity, authors advocate a modified theory of causability, according to which it is permissible for the parties to invoke abstract actions if this is not opposed by binding legal provisions.Artykuł przedstawia różne teorie dotyczące zasady kauzalności czynności prawnych przysparzających, obowiązującej w różnych kodyfikacjach prawa cywilnego. Zasada ta w ogólnym zarysie stanowi warunek ważności czynności prawnych przysparzających, wpływając na konstrukcję zobowiązań oraz przeniesienia własności. Wywodzące się jeszcze z prawa rzymskiego, a następnie rozwinięte przez postglosatorów oraz zwolenników szkoły prawa natury typy kauza, takie jak causa solvendi, donandi, aquirendi czy causa cavendi stały się zatem punktem odniesienia dla oceny ważności przysporzeń. Odnosząc się do intencjonalnego działania na płaszczyźnie intersubiektywnej w ujęciu filozofii analitycznej, autorzy opowiadają się za modyfikacją zasady kauzalności i dopuszczeniem możliwości kształtowania czynności oderwanych od przyczyny prawnej, o ile nie jest to sprzeczne z obowiązującymi przepisami

The effectiveness of styrene-maleic acid (SMA) copolymers for solubilisation of integral membrane proteins from SMA-accessible and SMA-resistant membranes

Solubilisation of biological lipid bilayer membranes for analysis of their protein complement has traditionally been carried out using detergents, but there is increasing interest in the use of amphiphilic copolymers such as styrene maleic acid (SMA) for the solubilisation, purification and characterisation of integral membrane proteins in the form of protein/lipid nanodiscs. Here we survey the effectiveness of various commercially-available formulations of the SMA copolymer in solubilising Rhodobacter sphaeroides reaction centres (RCs) from photosynthetic membranes. We find that formulations of SMA with a 2:1 or 3:1 ratio of styrene to maleic acid are almost as effective as detergent in solubilising RCs, with the best solubilisation by short chain variants ( < 30 kDa weight average molecular weight). The effectiveness of 10 kDa 2:1 and 3:1 formulations of SMA to solubilise RCs gradually declined when genetically-encoded coiled-coil bundles were used to artificially tether normally monomeric RCs into dimeric, trimeric and tetrameric multimers. The ability of SMA to solubilise reaction centre-light harvesting 1 (RC-LH1) complexes from densely packed and highly ordered photosynthetic membranes was uniformly low, but could be increased through a variety of treatments to increase the lipid:protein ratio. However, proteins isolated from such membranes comprised clusters of complexes in small membrane patches rather than individual proteins. We conclude that short-chain 2:1 and 3:1 formulations of SMA are the most effective in solubilising integral membrane proteins, but that solubilisation efficiencies are strongly influenced by the size of the target protein and the density of packing of proteins in the membrane

Cyanobacterial lipopolysaccharides and human health – a review

Cyanobacterial lipopolysaccharide/s (LPS) are frequently cited in the cyanobacteria literature as toxins responsible for a variety of heath effects in humans, from skin rashes to gastrointestinal, respiratory and allergic reactions. The attribution of toxic properties to cyanobacterial LPS dates from the 1970s, when it was thought that lipid A, the toxic moiety of LPS, was structurally and functionally conserved across all Gram-negative bacteria. However, more recent research has shown that this is not the case, and lipid A structures are now known to be very different, expressing properties ranging from LPS agonists, through weak endotoxicity to LPS antagonists. Although cyanobacterial LPS is widely cited as a putative toxin, most of the small number of formal research reports describe cyanobacterial LPS as weakly toxic compared to LPS from the Enterobacteriaceae. We systematically reviewed the literature on cyanobacterial LPS, and also examined the much lager body of literature relating to heterotrophic bacterial LPS and the atypical lipid A structures of some photosynthetic bacteria. While the literature on the biological activity of heterotrophic bacterial LPS is overwhelmingly large and therefore difficult to review for the purposes of exclusion, we were unable to find a convincing body of evidence to suggest that heterotrophic bacterial LPS, in the absence of other virulence factors, is responsible for acute gastrointestinal, dermatological or allergic reactions via natural exposure routes in humans. There is a danger that initial speculation about cyanobacterial LPS may evolve into orthodoxy without basis in research findings. No cyanobacterial lipid A structures have been described and published to date, so a recommendation is made that cyanobacteriologists should not continue to attribute such a diverse range of clinical symptoms to cyanobacterial LPS without research confirmation