4,438 research outputs found
Risk and Machine Protection for Stored Magnetic and Beam Energies
Risk is a fundamental consideration when designing electronic systems. For
most systems a view of risk can assist in setting design objectives, whereas
both a qualitative and quantitative understanding of risk is mandatory when
considering protection systems. This paper gives an overview of the risks due
to stored magnetic and beam energies in high-energy physics, and shows how a
risk-based approach can be used to design new systems mitigating these risks,
using a lifecycle inspired by IEC 61508. Designing new systems in high-energy
physics can be challenging as new and novel techniques are difficult to
quantify and predict. This paper shows how the same lifecycle approach can be
used in reverse to analyse existing systems, following their operation and
first experiences.Comment: 19 pages, contribution to the 2014 CAS - CERN Accelerator School:
Power Converters, Baden, Switzerland, 7-14 May 201
A 14-dimensional module for the symplectic group: orbits on vectors
Let F be a field, V a 6-dimensional F-vector space and f a nondegenerate alternating bilinear form on V. We consider a 14-dimensional module for the symplectic group Sp(V, f) congruent to Sp(6, F) associated with (V, f), and classify the orbits on vectors. For characteristic distinct from 2, this module is irreducible and isomorphic to the Weyl module of Sp(V, f) for the fundamental weight lambda(3). If the characteristic is 2, then the module is reducible as it contains an 8-dimensional submodule isomorphic to the spin module of Sp(V, f)
Immigration Policy reform: International Students and Higher Education
How has the rise in immigration around the world affected international students in obtaining student visas? Many states in the Global North are implementing restrictive immigration policies to combat the high influx of immigrants. Using the United Kingdom (UK) as a case study, I investigate how these policies have led to a decrease in the number of international students enrolled in higher education institutions (HEIs) throughout the UK. This has led to negative impacts on the higher education sector and economy, forcing politicians to reconsider and backtrack on immigration policies regarding international students in late 2017. Through the lens of the Liberal Paradox, I explain why a state is at odds between having restrictive and open policies towards immigrants. By studying the two policies and their effects in the UK and abroad, I look at why the UK government proposed new reforms to backtrack on the restrictive policies directed towards international students. I argue that public policy ideals, the policy’s effect on the economy and the higher education sector, and public opinion on the issue are the main drivers of this policy reversal, not even ten years after its initial adoption
Selecting asteroids for a targeted spectroscopic survey
Asteroid spectroscopy reflects surface mineralogy. There are few thousand
asteroids whose surfaces have been observed spectrally. Determining the surface
properties of those objects is important for many practical and scientific
applications, such as for example developing impact deflection strategies or
studying history and evolution of the Solar System and planet formation.
The aim of this study is to develop a pre-selection method that can be
utilized in searching for asteroids of any taxonomic complex. The method could
then be utilized im multiple applications such as searching for the missing
V-types or looking for primitive asteroids.
We used the Bayes Naive Classifier combined with observations obtained in the
course of the Sloan Digital Sky Survey and the Wide-field Infrared Survey
Explorer surveys as well as a database of asteroid phase curves for asteroids
with known taxonomic type. Using the new classification method we have selected
a number of possible V-type candidates. Some of the candidates were than
spectrally observed at the Nordic Optical Telescope and South African Large
Telescope.
We have developed and tested the new pre-selection method. We found three
asteroids in the mid/outer Main Belt that are likely of differentiated type.
Near-Infrared are still required to confirm this discovery. Similarly to other
studies we found that V-type candidates cluster around the Vesta family and are
rare in the mid/oter Main Belt.
The new method shows that even largely explored large databases combined
together could still be further exploited in for example solving the missing
dunite problem.Comment: accepted to A
TiB_2 and ZrB_2 diffusion barriers in GaAs Ohmic contact technology
The transition metal diboride compounds, ZrB_2 and TiB_2, interposed between Ni/Ge/Au Ohmic contact metallization on n‐type GaAs wafers and an overlying thick Au contact layer, have been investigated to evaluate their effectiveness in stabilizing the Ohmic contact by limiting the in‐diffusion of Au. All of the metal layers were e‐beam deposited except the ZrB_2 which was rf‐diode sputtered. The barrier layer thicknesses were 50 and 100 nm for the TiB_2 and the ZrB_2, respectively. Postdeposition alloying of the contacts was performed at 400, 425, or 450 °C. Auger electron spectroscopy depth profiling of the resultant Ohmic contacts demonstrates that the barrier layers effectively preclude penetration of Au to the Ohmic contact structure. Specific contact resistivities for such contacts are in the low 10^(−7) Ω cm^2 range; although some degradation of the contact resistivity is observed after long term annealing, the values of resistivities do not exceed 1.5×10^(−6) Ω cm^2 after 92 h at 350 °C
Physical and dynamical characterisation of low Delta-V NEA (190491) 2000 FJ10
We investigated the physical properties and dynamical evolution of Near Earth
Asteroid (NEA) (190491) 2000 FJ10 in order to assess the suitability of this
accessible NEA as a space mission target. Photometry and colour determination
were carried out with the 1.54 m Kuiper Telescope and the 10 m Southern African
Large Telescope during the object's recent favourable apparition in 2011-12.
During the earlier 2008 apparition, a spectrum of the object in the 6000-9000
Angstrom region was obtained with the 4.2 m William Herschel Telescope.
Interpretation of the observational results was aided by numerical simulations
of 1000 dynamical clones of 2000 FJ10 up to 10^6 yr in the past and in the
future. The asteroid's spectrum and colours determined by our observations
suggest a taxonomic classification within the S-complex although other
classifications (V, D, E, M, P) cannot be ruled out. On this evidence, it is
unlikely to be a primitive, relatively unaltered remnant from the early history
of the solar system and thus a low priority target for robotic sample return.
Our photometry placed a lower bound of 2 hrs to the asteroid's rotation period.
Its absolute magnitude was estimated to be 21.54+-0.1 which, for a typical
S-complex albedo, translates into a diameter of 130+-20 m. Our dynamical
simulations show that it has likely been an Amor for the past 10^5 yr. Although
currently not Earth-crossing, it will likely become so during the period 50 -
100 kyr in the future. It may have arrived from the inner or central Main Belt
> 1 Myr ago as a former member of a low-inclination S-class asteroid family.
Its relatively slow rotation and large size make it a suitable destination for
a human mission. We show that ballistic Earth-190491-Earth transfer
trajectories with Delta-V < 2 km s^-1 at the asteroid exist between 2052 and
2061.Comment: 2 Tables, 11 Figures, accepted for publication in Astronomy &
Astrophysic
Search for Rare Natural Decay Modes from 228-Th
This research was sponsored by the National Science Foundation Grant NSF PHy 87-1440
The Okun Misery Index in the European Union Countries from 2000 to 2009
The study is composed of four main parts and a summary. The first part, introduction, discusses various measures of the economic system's efficiency that are used in practice. Part two emphasises that the GDP per capita according to purchasing power parity still remains the most popular among those measures. Further, it presents the ranking of the European Union countries taking that measure into account, the research period being 1999-2009. Part three points out that it is also the level of poverty (misery) that determines the economic system's efficiency. That level can be measured by means of various indicators, among others, the so called HPI-2 index calculated by the UN. It will be the Okun misery index, however, computed as the sum of inflation and unemployment rates that will be presented as an alternative being of interest from the macroeconomic point of view. The ranking of the European Union member states according to that measure in the 2000-2004 and 2005-2009 periods will be provided in part four. The article will end in a summary containing synthetic conclusions drawn from earlier observations.Opracowanie składa się z czterech części zasadniczych i podsumowania. W punkcie pierwszym omówiono różnorodne mierniki sprawności systemu gospodarczego wykorzystywane w praktyce. W części drugiej podkreślono, iż nadal najpopularniejszym z nich jest PKB per capita według parytetu siły nabywczej. Zgodnie z tym miernikiem przedstawiono ranking państw Unii Europejskiej w latach 1999-2009. W punkcie trzecim podkreślono, że o sprawności systemu gospodarczego decyduje także poziom ubóstwa. Może być on mierzony różnymi wskaźnikami, m.in. tzw. indeksem HPI-2 obliczanym przez ONZ. Jako ciekawą z makroekonomicznego punktu widzenia alternatywę ukazano jednak miarę wskaźnika ubóstwa Okuna obliczanego poprzez zsumowanie stopy inflacji i stopy bezrobocia. Ranking państw Unii Europejskiej według tej miary w okresach 2000-2004 oraz 2005-2009 zaprezentowano w części czwartej. Całość zamknięto podsumowaniem, w którym zawarto syntetyczne wnioski z przeprowadzonych obserwacji
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