272,643 research outputs found
Den lysande återvinningen : - Sammanställning av återvinningslösningar för sällsynta jordartsmetaller (REEs) som förekommer i LED-lampor
No full textRare earth metals, REEs, which is a group of metallic elements, are used in LEDs for creating colored light. REEs are produced by mining in different countries, where China accounts for about 90% of global production. The recovery of REEs appearing in LED lights are now virtually non-existent and Stena Techno World AB has requested a study showing how the composition of REEs looks for LEDs with the aim to evaluate how a future recovery process might look. This project consisted of a literature review, interviews and field trips. REEs is present in extremely small quantities in each LED application, and this makes it very difficult to separate the REEs from the LED in a recycling process. This project has compiled the existing recycling solutions that are used for fluorescents, since the recovery process theoretically can be the same for the LED lights, if one ignores the fact that it is difficult to separate REEs from LED lights. A summary of the presence and quantity of REEs in LED lights with white lights presented in the results section of the project. In the results section is also reported a security strategy developed by the U.S. Department of Energy, where the aim of the strategy is to reduce dependence on China's REE resources. The discussion deals with the fact that a separation of REEs is difficult to achieve , and which aspects can justify an investment in recycling technology for REEs appearing in LED lights. The discussion also present calculations of how much of each REE present in the recycling loop of LED lights
On finiteness conditions for Rees matrix semigroups
No full textsummary:Let be a Rees matrix semigroup where is a semigroup, and are index sets, and is a matrix with entries from , and let be the ideal generated by all the entries of . If has finite index in , then we prove that is periodic (locally finite) if and only if is periodic (locally finite). Moreover, residual finiteness and having solvable word problem are investigated
Spain and Portugal / published by Longman, Rees, Orme, Brown and Green
No full text1 mapa. Mapa núm. 13. Pintat. Toponímia en anglès.21 x 28 c
Reply to Diesendorf, M. Comment on “Seibert, M.K.; Rees, W.E. Through the Eye of a Needle: An Eco-Heterodox Perspective on the Renewable Energy Transition. <i>Energies</i> 2021, <i>14</i>, 4508”
No full textWhen we published Seibert and Rees (2021) [...
Newsletter No. I
No full textNewsletter No. I written by Rees Odeil Bryant dated 1 March 1958. Bryant updates his readers on the final preparations for their travels to Nigeria
Rees cones and monomial rings of matroids
No full textAbstractUsing linear algebra methods we study certain algebraic properties of monomial rings and matroids. Let I be a monomial ideal in a polynomial ring over an arbitrary field. If the Rees cone of I is quasi-ideal, we express the normalization of the Rees algebra of I in terms of an Ehrhart ring. We introduce the basis Rees cone of a matroid (or a polymatroid) and study their facets. Some applications to Rees algebras are presented. It is shown that the basis monomial ideal of a matroid (or a polymatroid) is normal
(Table 1) Magnetic properties of specimens from DSDP Hole 68-503A
No full textMeasurements were made of the magnetic properties of 13 sediment samples from cores spanning the entire depth of Hole 503A. The principal aim was to make a preliminary assessment of the magnetic fabric of material obtained from hydraulic piston coring (HPC) which, though considerably bioturbated, might retain substantial traces of any depositional alignment of magnetic grains.
Earlier measurements on Deep Sea Drilling Project cores (Rees, 1971; Rees and Frederick, 1974; Hailwood and Sayre, 1979) suggested that the improved HPC sampling technique should, other things being equal, provide good magnetic fabric information. The Hole 503A sediments were known from shipboard measurements to possess comparatively strong stable remanence and therefore seemed likely subjects for this assessment
Equations of multi-Rees Algebras
No full textIn this thesis we describe the defining equations of certain multi-Rees algebras. First, we determine the defining equations of the multi-Rees algebra over a Noetherian ring when is an ideal of linear type. This generalizes a result of Ribbe and recent work of Lin-Polini and Sosa. Second, we describe the equations defining the multi-Rees algebra , where is a Noetherian ring containing a field and the ideals are generated by a subset of a fixed regular sequence
F-Rationality of Rees Algebras
No full textAbstractIn this paper, using the notion of the tight integral closure, we will give a criterion for F-rationality of Rees algebras of m-primary ideals in a Cohen–Macaulay local ring. As its application, we prove the following results: (1) In dimension two, if A is F-rational and I is integrally closed, then the Rees algebra R(I) is F-rational. On the other hand, in higher dimensions, we construct many examples of Cohen–Macaulay, normal Rees algebras which are not F rational. (2) If both A and R(I) are F-rational, then so is the extended Rees algebra R′(I). (3) If R(I) is F-rational and a(G(I))≠−1, then A is F-rational.On the other hand, using resolution of singularities, we will prove that a two-dimensional rational singularity always admits F-rational Rees algebras. In particular, this theorem gives another way than that devised by Watanabe (1997, J. Pure Appl. Algebra122, 323–328) to construct counterexamples to the Boutot-type theorem for F-rational rings
The equations of Rees algebras of ideals of almost-linear type
No full textL’àlgebra de Rees R(I) d’un ideal I d’un anell Noetherià local R juga un paper molt important en àlgebra commutativa i geometria algebraica, perquè Proj(R(I)) és l’explosió (blowup) de l’esquema afí Spec(R) al llarg del subesquema Spec(R/I). Fins avui dia, el problema de descriure les equacions de l’àlgebra de Rees d’ideals, així com altres àlgebres relacionades, com ara l’anell graduat associat G(I) o el con de la fibra F(I), s’ha mostrat molt rellevant per tal de comprendre els fenòmens que envolten aquestes àlgebres.
Les equacions de l’àlgebra de Rees R(I) són definibles com els elements del nucli Q d’una presentació polinòmica de R(I). Malgrat que aquest nucli pot dependre de la presentació escollida, no és difícil veure que els graus d’un sistema minimal de generadors homogenis de Q no depenen de la presentació.
El màxim entre els graus dels generadors homogenis minimals de qualsevol presentació polinòmica, conegut com a tipus de relació, denotat rt(I), dóna una mesura senzilla – i tanmateix útil en molts contextos – de la complexitat de l’àlgebra de Rees. Els ideals tals que rt(I)=1, anomenats ideals de tipus lineal, han sigut intensament estudiats en les darreres dècades i encara avui dia romanen una font de problemes i exemples interessants.
En aquest treball encarem el problema de descriure les equacions de R(I) quan l’ideal I és de la forma I=(J,y), on J és un ideal de tipus lineal: d’aquests ideals objecte del nostre estudi en direm ideals de tipus quasi-lineal.
Els resultats principals d’aquest treball rauen en dues aproximacions diferents vers el problema. Per una banda, donem una descripció explícita de les equacions dels ideals I de la forma I=(J,y) quan els generadors de J satisfan l’anul·lació d’un cert grup d’homologia de Koszul. Si bé l’anul·lació d’aquesta homologia no implica automàticament que J sigui de tipus lineal, sí n’és una condició molt propera i també ens permet contemplar altres classes d’ideals. El nostre Teorema A ens permet recuperar, unificar i estendre resultats ja coneguts en el context d’ideals de tipus quasi-lineal deguts a Vasconcelos, Huckaba, Trung, Heinzer i Kim.
Sigui α: S(I) → R(I) el morfisme graduat canònic des de l’àlgebra simètrica de I vers l’àlgebra de Rees de I. El segon resultat principal d’aquest treball demostra que l’injectivitat d’una sola component graduada de α és condició suficient per a garantir l’injectivitat de la resta de les components graduades inferiors si I és un ideal de tipus quasi-lineal. En particular, el nostre resultat respon afirmativament i de manera parcial a una pregunta formulada per Tchernev.
Val a dir que el nostre resultat funciona per a tots els ideals de tipus quasi-lineal i encara per a ideals una mica més generals.
Finalment, donem exemples que il·lustren l’abast i les aplicacions de la col·lecció de resultants presentats. L’autor també dóna una col·lecció de càlculs i exemples que motiven presents i futures activitats de recerca.The Rees algebra R(I) = R[It] of an ideal I of a Noetherian local ring R plays a major role in commutative algebra and in algebraic geometry, since Proj(R(I)) is the blowup of the affine scheme Spec(R) along the closed subscheme Spec(R/I).
So far, the problem of describing the equations of Rees algebras of ideals, as well as other related algebras, has shown to be relevant in order to further understand these major algebraic objects. The equations of R(I) arise as the elements in the kernel Q of a symmetric presentation of R(I). While this kernel may differ from one presentation to another, the degrees of a minimal generating set of homogeneous elements are known to be independent from the chosen presentation. The top degree among such generating sets, known as the relation type and denoted by rt(I), is a coarse measurement of the complexity of the underlying Rees algebra which is nonetheless a useful numerical invariant. The ideals I such that rt(I) = 1, known as ideals of linear type, have been intensely studied so far.
In this dissertation, we tackle the problem of describing the equations of R(I) for I =(J, y), with J being of linear type, i.e., for ideals of linear type up to one minimal generator. Throughout, such ideals will be referred to as ideals of almost-linear type.
The main results of this work stem from two different approaches towards the problem. In Theorem A, we give a full description of the equations of Rees algebras of ideals of the form I = (J,y), with J satisfying an homological vanishing condition. Theorem A permits us to recover and extend well-known results about families of ideals fulfilling the almost-linear type condition due to Vasconelos, Huckaba, Trung, Heinzer and Kim, among others.
Let α: S(I)→R(I) be the canonical morphism from the symmetric algebra of I to the Rees algebra of I. In Theorem B, we prove that the injectivity of a single component of α: S(I)→R(I) propagates downwards, provided I is of almost-linear type. In particular, this result gives a partial answer to a question posed by Tchernev.
Finally, packs of examples are introduced, which illustrate the scope and applications of each of the results presented. The author also gives a collection of computations and examples which motivate ongoing and future research.DOCTORAT EN MATEMÀTICA APLICADA (Pla 1998
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