EVALUATION OF MAGNESIUM AS A HALL THRUSTER PROPELLANT

In this study, the use of magnesium as a Hall thruster propellant was evaluated. A xenon Hall thruster was modified such that magnesium propellant could be loaded into the anode and use waste heat from the thruster discharge to drive the propellant vaporization. A control scheme was developed, which allowed for precise control of the mass flow rate while still using plasma heating as the main mechanism for evaporation. The thruster anode, which also served as the propellant reservoir, was designed such that the open area was too low for sufficient vapor flow at normal operating temperatures (i.e. plasma heating alone). The remaining heat needed to achieve enough vapor flow to sustain thruster discharge came from a counter-wound resistive heater located behind the anode. The control system has the ability to arrest thermal runaway in a direct evaporation feed system and stabilize the discharge current during voltage-limited operation. A proportional-integral-derivative control algorithm was implemented to enable automated operation of the mass flow control system using the discharge current as the measured variable and the anode heater current as the controlled parameter. Steady-state operation at constant voltage with discharge current excursions less than 0.35 A was demonstrated for 70 min. Using this long-duration method, stable operation was achieved with heater powers as low as 6% of the total discharge power. Using the thermal mass flow control system the thruster operated stably enough and long enough that performance measurements could be obtained and compared to the performance of the thruster using xenon propellant. It was found that when operated with magnesium, the thruster has thrust ranging from 34 mN at 200 V to 39 mN at 300 V with 1.7 mg/s of propellant. It was found to have 27 mN of thrust at 300 V using 1.0 mg/s of propellant. The thrust-to-power ratio ranged from 24 mN/kW at 200 V to 18 mN/kW at 300 volts. The specific impulse was 2000 s at 200 V and upwards of 2700 s at 300 V. The anode efficiency was found to be ~23% using magnesium, which is substantially lower than the 40% anode efficiency of xenon at approximately equivalent molar flow rates. Measurements in the plasma plume of the thruster—operated using magnesium and xenon propellants—were obtained using a Faraday probe to measure off-axis current distribution, a retarding potential analyzer to measure ion energy, and a double Langmuir probe to measure plasma density, electron temperature, and plasma potential. Additionally, the off axis current distributions and ion energy distributions were compared to measurements made in krypton and bismuth plasmas obtained in previous studies of the same thruster. Comparisons showed that magnesium had the largest beam divergence of the four propellants while the others had similar divergence. The comparisons also showed that magnesium and krypton both had very low voltage utilization compared to xenon and bismuth. It is likely that the differences in plume structure are due to the atomic differences between the propellants; the ionization mean free path goes down with increasing atomic mass. Magnesium and krypton have long ionization mean free paths and therefore require physically larger thruster dimensions for efficient thruster operation and would benefit from magnetic shielding.

Effect of peritoneal fluid from endometriosis patients on neuroblastoma cells in culture

AIM: Endometriosis is often associated with lower abdominal pain, dysmenorrhea, dyspareunia, and chronic pelvic pain. There is no correlation between the extent of endometriosis and the intensity of pain. The mechanism of pain in endometriosis is unknown. The aim of our study was to investigate the influence of peritoneal fluid (PF) from endometriosis patients on cultured neural cells that are the morphological basis of nociception, and to determine whether there was a relationship between the rAFS staging and an elevation of TGF-beta1 production by these cells. METHODS: Different human neuroblastoma cell lines were grown to 3/4 confluence and then cultured in presence of PF pooled according to the presence of no, mild, or severe endometriosis. After 6 and 24 h of incubation, the morphological changes were assessed and the metabolic activity was determined. RESULTS: The different cell lines showed strongly varying proliferation and aggregation patterns. The metabolic activity was also varying between cell lines, but no consistently increased cell turnover in the PF when compared with the control medium nor associated to a particular, endometriosis-derived PF pool could be shown. In this experimental setting, we have observed that the cell proliferation in the presence of PF was inhibited, and not enhanced as it might have been expected. Measurement of TGF-beta1 showed higher production rates for this cytokine under exposure to PF than in controls for some but not all tested cell lines, but there was no association with the stage (rAFS) of the disease. CONCLUSION: The neuronal cell culture model may become a useful tool to investigate the endometriosis-derived pain, but different endpoints and cell lines may have to be introduced.

The Implementation of Full-time Schools: The Situation in the Federal State of Sao Paulo (Brazil)

During the past years, Brazil has been mentioned internationally as a one of the so-called BRICs (Brazil, Russia, India and China). These countries have been taking increasing space in the economical and political global scenarios in the XXI century. The facts that they possess a vast territory and stand among the highest populated countries increase their relevance within the United Nations. Besides, three of them constitute nuclear powers and two of them belong to the United Nations Security Council. Brazil has significantly participated in forums such as WTO and UNO, representing central political articulation and stability to Latin America and in the structuring and growth of MERCOSUL (Brazil, Argentina, Uruguay, Paraguay and Venezuela). Once again among the ten greatest economies of the world, the country has launched ambitious poverty-fighting programs helping more than 20 million people in the last years, such as the “Bolsa Família” (Familienstipendium) Program or and its complements). Nevertheless, Latin American countries are far from generating structural funds as the “European Social Fund” to assist specific demands of big cities as Sao Paulo and Buenos Aires. The commitments are restricted to commercial areas and bring nothing but slow and scarce advances to education or infra-structure and to the integration of systems related to these areas.

Intracoronary Optical Coherence Tomography and Histology of Overlapping Everolimus-Eluting Bioresorbable Vascular Scaffolds in a Porcine Coronary Artery Model

OBJECTIVES: This study sought to assess the vascular response of overlapping Absorb stents compared with overlapping newer-generation everolimus-eluting metallic platform stents (Xience V [XV]) in a porcine coronary artery model. BACKGROUND: The everolimus-eluting bioresorbable vascular scaffold (Absorb) is a novel approach to treating coronary lesions. A persistent inflammatory response, fibrin deposition, and delayed endothelialization have been reported with overlapping first-generation drug-eluting stents. METHODS: Forty-one overlapping Absorb and overlapping Xience V (XV) devices (3.0 × 12 mm) were implanted in the main coronary arteries of 17 nonatherosclerotic pigs with 10% overstretch. Implanted coronary arteries were evaluated by optical coherence tomography (OCT) at 28 days (Absorb n = 11, XV n = 7) and 90 days (Absorb n = 11, XV n = 8), with immediate histological evaluation following euthanasia at the same time points. One animal from each time point was evaluated with scanning electron microscopy alone. A total of 1,407 cross sections were analyzed by OCT and 148 cross sections analyzed histologically. RESULTS: At 28 days in the overlap, OCT analyses indicated 80.1% of Absorb struts and 99.4% of XV struts to be covered (p < 0.0001), corresponding to histological observations of struts with cellular coverage of 75.4% and 99.6%, respectively (p < 0.001). Uncovered struts were almost exclusively related to the presence of "stacked" Absorb struts, that is, with a direct overlay configuration. At 90 days, overlapping Absorb and overlapping XV struts demonstrated >99% strut coverage by OCT and histology, with no evidence of a significant inflammatory process, and comparable % volume obstructions. CONCLUSIONS: In porcine coronary arteries implanted with overlapping Absorb or overlapping XV struts, strut coverage is delayed at 28 days in overlapping Absorb, dependent on the overlay configuration of the thicker Absorb struts. At 90 days, both overlapping Absorb and overlapping XV have comparable strut coverage. The implications of increased strut thickness may have important clinical and design considerations for bioresorbable platforms.

The Life and Times of Bills

Time is one of the scarcest resources in modern parliaments. In parliamentary systems of government the control of time in the chamber is a significant power resource enjoyed – to varying degrees – by parliamentary majorities and the governments they support. Minorities may not be able to muster enough votes to stop bills, but they may have – varying degrees of – delaying powers enabling them to extract concessions from majorities attempting to get on with their overall legislative programme. This paper provides a comparative analysis of the dynamics of the legislative process in 17 West European parliaments from the formal initiation of bills to their promulgation. The ‘biographies’ of a sample of bills are examined using techniques of event-history analysis (a) charting the dynamics of the legislative process both across the life-times of individual bills and different political systems and (b) examining whether, and to what extent, parliamentary rules and some general regime attributes influence the dynamics of this process, speeding up or delaying the passage of legislation. Using a veto-points framework and transaction cost politics as a theoretical framework, the quantitative analyses suggest a number of counter-intuitive findings (e.g., the efficiency of powerful committees) and cast doubt on some of the claims made by Tsebelis in his veto-player model.

Bond strength of adhesives to dentin contaminated with smoker's saliva.

The purpose of this study was to determine the effects of contamination with smoker's and non-smoker's saliva on the bond strength of resin composite to superficial dentin using different adhesive systems. The interfacial structure between the resin and dentin was evaluated for each treatment using environmental scanning electron microscopy (ESEM). Freshly extracted human molars were ground with 600-grit SiC paper to expose the superficial dentin. Adhesives [One-Up-Bond-F-Plus (OUFP) and Adper-Prompt-L-Pop (APLP)] and resin composite (TPHSpectrum) were bonded to the dentin (n = 8/group, 180 total specimens) under five surface conditions: control (adhesive applied following manufacturers' instructions); saliva, then 5-s air dry, then adhesive; adhesive, saliva, 5-s air dry; adhesive, saliva, 5-s water rinse, 5-s air dry (ASW group); and adhesive, saliva, 5-s water rinse, 5-s air dry, reapply adhesive (ASWA group). After storage in water at 37 degrees C for 24 h, the specimens were debonded under tension at a speed of 0.5 mm/min. ESEM photomicrographs of the dentin/adhesive interfaces were taken. Mean bond strength ranged from 8.1 to 24.1 MPa. Fisher's protected least significant difference (P = 0.05) intervals for critical adhesive, saliva, and surface condition differences were 1.3, 1.3, and 2.1 MPa, respectively. There were no significant differences in bond strength to dentin between contamination by smoker's and nonsmoker's saliva, but bond strengths were significantly different between adhesive systems, with OUFP twice as strong as APLP under almost all conditions. After adhesive application and contamination with either smoker's or nonsmoker's saliva followed by washing and reapplication of the adhesive (ASWA group), the bond strength of both adhesive systems was the same as that of the control group.

Implementation of an Anthropomorphic Phantom for the Evaluation of Proton Therapy Treatment Procedures

With an increasing number of institutions offering proton therapy, the number of multi-institutional clinical trials involving proton therapy will also increase in the coming years. The Radiological Physics Center monitors sites involved in clinical trials through the use of site visits and remote auditing with thermoluminescent dosimeters (TLD) and mailable anthropomorphic phantoms. Currently, there are no heterogeneous phantoms that have been commissioned to evaluate proton therapy. It was hypothesized that an anthropomorphic pelvis phantom can be designed to audit treatment procedures (patient simulation, treatment planning and treatment delivery) at proton facilities to confirm agreement between the measured dose and calculated dose within 5%/3mm with a reproducibility of 3%. A pelvis phantom originally designed for use with photon treatments was retrofitted for use in proton therapy. The relative stopping power (SP) of each phantom material was measured. Hounsfield Units (HU) for each phantom material were measured with a CT scanner and compared to the relative stopping power calibration curve. The tissue equivalency for each material was calculated. Two proton treatment plans were created; one which did not correct for material SP differences (Plan 1) and one plan which did correct for SP differences (Plan 2). Film and TLD were loaded into the phantom and the phantom was irradiated 3 times per plan. The measured values were compared to the HU-SP calibration curve and it was found that the stopping powers for the materials could be underestimated by 5-10%. Plan 1 passed the criteria for the TLD and film margins with reproducibility under 3% between the 3 trials. Plan 2 failed because the right-left film dose profile average displacement was -9.0 mm on the left side and 6.0 mm on the right side. Plan 2 was intended to improve the agreements and instead introduced large displacements along the path of the beam. Plan 2 more closely represented the actual phantom composition with corrected stopping powers and should have shown an agreement between the measured and calculated dose within 5%/3mm. The hypothesis was rejected and the pelvis phantom was found to be not suitable to evaluate proton therapy treatment procedures.

In vitro staining effects of stannous fluoride and sodium fluoride on ceramic material.

STATEMENT OF PROBLEM: Long-term fluoride application on the teeth of patients receiving radiation therapy for head and neck tumors results in excessive staining and roughening of ceramic restorations. PURPOSE: The purpose of this in vitro study was to compare the staining effects of 2 fluoride treatments on ceramic disks by simulating 1 year of clinical exposure at 10 minutes per day. In addition, 2 different surface preparations were tested. MATERIAL AND METHODS: Eighty ceramic disks (IPS Empress), 20 x 2 mm, were fabricated. Half of the disks were glazed, and the remaining disks were polished. All disks were brushed for 3 minutes with a soft-bristle power toothbrush and mild dentifrice (baseline) and were immersed in 1 of the 2 fluoride products (0.4% SnF(2), Gel-Kam Gel, or 1.1% NaF, Prevident 5000) for 10 days (n=20). Means and standard deviations of color change (Delta E), surface roughness (Ra, um), and surface gloss (GU) of the ceramic material were measured with a reflection spectrophotometer, a profilometer, and a gloss meter, respectively, at baseline and after fluoride treatment. Two- and 3-way ANOVA (alpha=.05), with surface preparation (polished vs. glazed) and fluoride treatment (0.4% SnF(2) or 1.1% NaF) as independent variables and condition (baseline vs. after fluoride treatment) as a repeated measure, was used to analyze the data. Fisher's PLSD intervals (alpha=.05) were calculated for comparisons among the means. RESULTS: The polished specimens had significantly higher Delta E values, significantly higher surface gloss values, and significantly lower surface roughness values than the glazed specimens before fluoride treatment (P<.001). After both fluoride treatments, ceramic disks exhibited significantly higher surface roughness values when polished and significantly lower surface gloss values when glazed or polished (P<.001). The glazed specimens presented significantly higher surface roughness (P<.001) and lower surface gloss values (P<.001) when treated with 0.4% SnF(2) as compared to NaF. For the polished specimens, there was no significant difference in surface roughness and surface gloss values between the 2 fluoride treatments. CONCLUSIONS: Use of 0.4% SnF(2) and 1.1% NaF gels, in vitro, caused significant color change in the polished IPS Empress ceramic disks. Polishing of the ceramic surface before immersion in either fluoride agent caused the ceramic tested to be more resistant to etching by the 2 solutions tested. The NaF caused less deterioration of the porcelain surface and was less stain inducing than SnF(2).

Shear bond strength of four different esthetic brackets.

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Influence of blood contamination on bond strength of a self-etching system.

OBJECTIVES: To detect the influence of blood contamination (BC) on the bond strength (BS) of a self-etching bonding system (SES) to enamel and dentine. METHODS: 25 human molars were longitudinally sectioned on the mesio-distal axis in order to obtain 50 specimens, which were embedded in acrylic resin. At first, the specimens were ground to expose a flat surface of enamel, and a bond strength test was performed. Afterwards, the samples were ground again in order to obtain a flat surface of dentine. Ten groups (total: n=100) were assigned according to substrate (enamel and dentine), step in the bonding sequence when contamination occurred (before the acidic primer and after the bonding resin), and contamination treatment (dry or rinse and dry procedure). Fresh human blood was introduced either before or after SES application (Clearfil SE Bond) and treated with air drying, or by rinsing and drying following application. Composite resin (Filtek Z-250,3M ESPE) was applied as inverted, truncated cured cones that were debonded in tension. RESULTS: The mean tensile BS values (MPa) for enamel/dentine were 19.4/23.0 and 17.1/10.0 for rinse-and-dry treatment (contamination before and after SES, respectively); while the measurements for the dry treatment, 16.2/23.3 and 0.0/0.0 contamination before and after SES, respectively. CONCLUSIONS: It was determined that blood contamination impaired adhesion to enamel and dentine when it occurred after bond light curing. Among the tested contamination treatments, the rinse-and-dry treatment produced the highest bond strength with BC after SES application, but it was not sufficient to recover the BS in the contamination-free group.

The EU’s Choice of Regulatory Venues for Trade Negotiations: A Tale of Agency Power?

This article focuses on the EU’s strategy for choosing regulatory venues to negotiate trade agreements. It analyses the existence of a clear venue hierarchy since the late 1990s and the recent change leading to a blurring of any clear preference for using bilateral, inter-regional or multilateral settings. The article challenges domestic explanations of the EU’s choice of venue, stressing the autonomy of the Commission as a major factor. Using a principal-agent framework, it shows that the Commission’s agenda-setting powers, the existence of interest divergence among principals (e.g. Member States, business groups) and the multi-level system facilitate agency.

Agents, Trustees, and International Courts: Nomination and Appointment of Judicial Candidates in the WTO Appellate Body

Scholars have increasingly theorized, and debated, the decision by states to create and delegate authority to international courts, as well as the subsequent autonomy and behavior of those courts, with principal–agent and trusteeship models disagreeing on the nature and extent of states’ influence on international judges. This article formulates and tests a set of principal–agent hypotheses about the ways in which, and the conditions under which, member states are able use their powers of judicial nomination and appointment to influence the endogenous preferences of international judges. The empirical analysis surveys the record of all judicial appointments to the Appellate Body (AB) of the World Trade Organization over a 15-year period. We present a view of an AB appointment process that, far from representing a pure search for expertise, is deeply politicized and offers member-state principals opportunities to influence AB members ex ante and possibly ex post. We further demonstrate that the AB nomination process has become progressively more politicized over time as member states, responding to earlier and controversial AB decisions, became far more concerned about judicial activism and more interested in the substantive opinions of AB candidates, systematically championing candidates whose views on key issues most closely approached their own, and opposing candidates perceived to be activist or biased against their substantive preferences. Although specific to the WTO, our theory and findings have implications for the judicial politics of a large variety of global and regional international courts and tribunals.

Trade versus Culture : The Policy of Cultural Exception and the World Trade Organization

This chapter is a contribution to the Palgrave Handbook of European Media Policy (co-edited by Pauwels, Donders & Loisen). It is the chapter’s purpose to examine the proponents of the cultural exception policy, their strategies and demands, and to explore how they came to be reflected in the law and policy of the World Trade Organization (WTO). The chapter also looks at the current state of affairs, as although WTO law has not undergone any substantial amendments since its entry into force in 1995, the media landscape has in the meantime been truly transformed, in some aspects in a revolutionary manner. The broader picture of global governance has not remained still either, with new and emergent powers, changing mechanisms of rule-making and taking.

New Philology and the Biogenetics of Texts

The discussion on the New Philology triggered by French and North American scholars in the last decade of the 20th century emphasized the material character of textual transmission inside and outside the written evidences of medieval manuscripts by downgrading the active role of the historical author. However, the reception of the ideas propagated by the New Philology adherents was rather divided. Some researchers considered it to be the result of an academic “crisis” (R.T. Pickens) or questioned its innovative status (K. Stackmann: “Neue Philologie?”); others appreciated the “new attitudes to the page” it had brought to mind (J. Bumke after R.H. and M.A, Rouse) or even saw a new era of the “powers of philology” evoked (H.-U. Gumbrecht). Besides the debates on the New Philology another concept of textual materiality strengthened in the last decade, maintaining that textual alterations somewhat relate to biogenetic mutations. In a matter of fact, phenomena such as genetic and textual variation, gene recombination and ‘contamination’ (the mixing of different exemplars in one manuscript text) share common features. The paper discusses to what extent the biogenetic concepts can be used for evaluating manifestations of textual production (as the approach of ‘critique génétique’ does) and of textual transmission (as the phylogenetic analysis of manuscript variation does). In this context yet the genealogical concept of stemmatology – the treelike representation of textual development abhorred by the New Philology adepts – might prove to be useful for describing the history of texts. The textual material to be analyzed will be drawn from the Parzival Project, which is currently preparing a new electronic edition of Wolfram von Eschenbach’s Parzival novel written shortly after 1200 and transmitted in numerous manuscripts up to the age of printing. Researches of the project have actually resulted in suggesting that the advanced knowledge of the manuscript transmission yields a more precise idea on the author’s own writing process.

Contrasts, Contacts, and Interconnections — Tel Kinrot as an Early Iron Age Key Site in the Northern Jordan Rift Valley at the Dawn of the 1st Millennium BCE

Ancient Kinneret (Tēl Kinrōt [Hebrew]; Tell el-ʿOrēme [Arabic]) is located on a steep limestone hill on the northwestern shores of the Sea of Galilee (2508.7529 [NIG]). The site, whose settlement history began sometime during the Pottery-Neolithic or the early Chalcolithic period, is emerging as one of the major sites for the study of urban life in the Southern Levant during the Early Iron Age (c. 1130–950 BCE). Its size, accessibility by major trade routes, and strategic location between different spheres of cultural and political influence make Tēl Kinrōt an ideal place for studying the interaction of various cultures on urban sites, as well as to approach questions of ethnicity and regionalism during one of the most debated periods in the history of the ancient Levant. The paper will briefly discuss the settlement history of the site during the Early Iron Age. However, the main focus will lie on the material culture of the late Iron Age IB city that rapidly evolved to a regional center during the transition from the 11th to the 10th century BCE. During this period, ancient Kinneret features a multitude of cultural influences that reach from Egypt via the Central Hill Country until the Northern parts of Syria and the Amuq region. While there are indisputably close ties with the ‘Aramaean’ realm, there are also strong indications that there were – at the same time – vivid socio-economic links with the West, i.e. the Southern and Northern Mediterranean coasts and their hinterland. It will be argued that the resulting ‘cultural blend’ is a typical characteristic of the material culture of the Northern Jordan Rift Valley in the advent of the emerging regional powers of the Iron Age II.