6,159 research outputs found
Effects of typhoons on gelatinous carnivore zooplankton off Northern Taiwan
We examine the effect of typhoons, as potential drivers of nutrient pulse events, on gelatinous carnivore zooplankton. The period investigated spanned from 2007 to 2010, where seasonal abundance and taxonomic composition of the gelatinous zooplankton community was recorded off North Taiwan. Typhoon effects were assessed in the abundance, diversity and species richness of the gelatinous carnivore populations. Significant associations between typhoons and gelatinous carnivores were found in time delays varying from 3 to 25 days, but no association was identified for longer time intervals. Generally, a decrease in species richness occurred during the summer season, and this was accentuated in 2008, shortly after typhoons events. We hypothesize that typhoons might act as resource pulse triggers probably enhancing open niches for opportunistic carnivore zooplankton groups
Stereoselectivity in Metallocene-Catalyzed Coordination Polymerization of Renewable Methylene Butyrolactones: From Stereo-random to Stereo-perfect Polymers
Coordination polymerization of renewable
α-methylene-γ-(methyl)butyrolactones by chiral C2-symmetric
zirconocene catalysts produces stereo-random,
highly stereo-regular, or perfectly stereo-regular polymers,
depending on the monomer and catalyst structures.
Computational studies yield a fundamental understanding
of the stereocontrol mechanism governing these new
polymerization reactions mediated by chiral metallocenium
catalysts
Lessons Learned Migrating CUDA to SYCL: A HEP Case Study with ROOT RDataFrame
The world's largest particle accelerator, located at CERN, produces petabytes
of data that need to be analysed efficiently, to study the fundamental
structures of our universe. ROOT is an open-source C++ data analysis framework,
developed for this purpose. Its high-level data analysis interface, RDataFrame,
currently only supports CPU parallelism. Given the increasing heterogeneity in
computing facilities, it becomes crucial to efficiently support GPGPUs to take
advantage of the available resources. SYCL allows for a single-source
implementation, which enables support for different architectures. In this
paper, we describe a CUDA implementation and the migration process to SYCL,
focusing on a core high energy physics operation in RDataFrame --
histogramming. We detail the challenges that we faced when integrating SYCL
into a large and complex code base. Furthermore, we perform an extensive
comparative performance analysis of two SYCL compilers, AdaptiveCpp and DPC++,
and the reference CUDA implementation. We highlight the performance bottlenecks
that we encountered, and the methodology used to detect these. Based on our
findings, we provide actionable insights for developers of SYCL applications
Lessons Learned Migrating CUDA to SYCL:A HEP Case Study with ROOT RDataFrame
The world's largest particle accelerator, located at CERN, produces petabytes of data that need to be analysed efficiently, to study the fundamental structures of our universe. ROOT is an open-source C++ data analysis framework, developed for this purpose. Its high-level data analysis interface, RDataFrame, currently only supports CPU parallelism. Given the increasing heterogeneity in computing facilities, it becomes crucial to efficiently support GPGPUs to take advantage of the available resources. SYCL allows for a single-source implementation, which enables support for different architectures. In this paper, we describe a CUDA implementation and the migration process to SYCL, focusing on a core high energy physics operation in RDataFrame -- histogramming. We detail the challenges that we faced when integrating SYCL into a large and complex code base. Furthermore, we perform an extensive comparative performance analysis of two SYCL compilers, AdaptiveCpp and DPC++, and the reference CUDA implementation. We highlight the performance bottlenecks that we encountered, and the methodology used to detect these. Based on our findings, we provide actionable insights for developers of SYCL applications
Weighted Barycentric Sets and Singular Liouville Equations on Compact Surfaces
Given a closed two dimensional manifold, we prove a general existence result
for a class of elliptic PDEs with exponential nonlinearities and negative Dirac
deltas on the right-hand side, extending a theory recently obtained for the
regular case. This is done by global methods: since the associated Euler
functional is in general unbounded from below, we need to define a new model
space, generalizing the so-called space of formal barycenters and
characterizing (up to homotopy equivalence) its very low sublevels. As a
result, the analytic problem is reduced to a topological one concerning the
contractibility of this model space. To this aim, we prove a new functional
inequality in the spirit of [16] and then we employ a min-max scheme based on a
cone-style construction, jointly with the blow-up analysis given in [5] (after
[6] and [8]). This study is motivated by abelian Chern- Simons theory in
self-dual regime, or from the problem of prescribing the Gaussian curvature in
presence of conical singularities (hence generalizing a problem raised by
Kazdan and Warner in [26]).Comment: to appear on Journal of Functional Analysis. One proof in Section 3
has been simplified with respect to the previous version, while Section 6 (on
open problems) has been substantially improved. At the end on the
Introduction, the complete proof of the topological conjecture given in
Section 6 (to appear in a forthcoming paper) is announce
Sudanske dvosupnice kao alternativni izvor vlakana za proizvodnju celuloze i papira
The suitability of the stems from two Sudanese dicotyledonous annual plants, namely castor bean (Ricinus communis) and Leptadenia pyrotechnica (L. pyrotechnica) were investigated for pulp and papermaking. Chemical compositions, elemental analysis, fiber dimensions, paper physical properties and morphology revealed a relatively high α-cellulose content (46.2 and 44.3 %) and low lignin (19.7 and 21.7 %) in the stems of castor bean and L. pyrotechnica, respectively. The average fiber length of castor bean and L. pyrotechnica is 0.80 and 0.70 mm with fiber width of 16.30 μm and 18.20 μm, respectively, which makes them acceptable candidates. Soda-AQ pulping of castor bean stem led to a higher pulp yield of 43.2 % at kappa number 18.2 compared to 40.3 % at kappa 20.3 for L. pyrotechnica. This yield is less than that obtained for wood plants and similar to that observed for annual plants. Paper handsheets produced from castor bean showed better mechanical properties than L. pyrotechnica. SEM images indicated that the produced papers were quite homogeneous, compact, closely packed, and well assembled.U radu je opisano istraživanje prikladnosti stabljika dviju sudanskih jednogodišnjih biljaka dvosupnica, ricinusa (Ricinus communis) i Leptadenia pirotechnica za dobivanje celulozu i proizvodnju papira. Kemijski sastav, elementarna analiza, dimenzije vlakana, fizikalna svojstva papira i morfologija pokazali su da je u stabljikama ricinusa i L. pyrotechnica relativno visok sadržaj α-celuloze (46,2 i 44,3 %) i nizak sadržaj lignina (19,7 i 21,7 %). Prosječna duljina vlakana ricinusa i L. pirotechnice iznosi 0,80 i 0,70 mm, a širina vlakana im je od 16,30 μm i 18,20 μm, što ih čini prihvatljivima za proizvodnju celuloze i papira. Sulfatnim je postupkom od stabljika ricinusa dobiven veći prinos celuloze (43,2 %) pri kappa broju 18,2 u usporedbi s prinosom celuloze (40,3 %) pri kappa broju 20,3, koji je dobiven pri proizvodnji celuloze od stabljika L. pyrotechnice. Dobiveni prinos manji je od prinosa koji se postiže proizvodnjom celuloze od drvenastih biljaka i jednak je prinosu koji se ostvaruje proizvodnjom celuloze od jednogodišnjih biljaka. Listovi papira proizvedeni od ricinusa pokazali su bolja mehanička svojstva od papira proizvedenoga od stabljika L. pyrotechnice. Slike dobivene skenirajućim elektronskim mikroskopom (SEM) pokazuju da su proizvedeni papiri bili posve homogeni, kompaktni, zbijeni i dobro sastavljeni
Accurate Kohn-Sham auxiliary system from the ground state density of solids
The Kohn-Sham (KS) system is an auxiliary system whose effective potential is
unknown in most cases. It is in principle determined by the ground state
density, and it has been found numerically for some low-dimensional systems by
inverting the KS equations starting from a given accurate density. For solids,
only approximate results are available. In this work, we determine accurate
exchange correlation (xc) potentials for Si and NaCl using the ground state
densities obtained from Auxiliary Field Quantum Monte Carlo calculations. We
show that these xc potentials can be rationalized as an ensemble of
environment-adapted functions of the local density. The KS band structure can
be obtained with high accuracy. The true KS band gap turns out to be larger
than the prediction of the local density approximation, but significantly
smaller than the measurable photoemission gap, which confirms previous
estimates. Finally, our findings show that the conjecture that very different
xc potentials can lead to very similar densities and other KS observables is
true also in solids, which questions the meaning of details of the potentials
and, at the same time, confirms the stability of the KS system
Autophagy occurs upstream or parallel to the apoptosome during histolytic cell death
Histolysis refers to a widespread disintegration of tissues that is morphologically distinct from apoptosis and often associated with the stimulation of autophagy. Here, we establish that a component of the apoptosome, and pivotal regulator of apoptosis, is also required for histolytic cell death. Using in vivo and ex vivo assays, we demonstrate a global apoptogenic requirement for dark, the fly ortholog of Apaf1, and show that a required focus of dark– organismal lethality maps to the central nervous system. We further
demonstrate that the Dark protein itself is a caspase substrate and find that alterations of this cleavage site produced the first hypermorphic point mutation within the Apaf1/Ced-4 gene family. In a model of ‘autophagic cell death’, dark was essential for histolysis but dispensable for characteristic features of the autophagic program, indicating that the induction of autophagy occurs upstream or parallel to histolytic cell death. These results demonstrate that stimulation of autophagy per se is not a ‘killing event’ and, at the same time, establish that common effector pathways, regulated by the apoptosome, can underlie morphologically distinct forms of programmed cell death
Unusual C–C Bond Cleavage in the Formation of Amine-Bis(phenoxy) Group 4 Benzyl Complexes: Mechanism of Formation and Application to Stereospecific Polymerization
Group 4 tetrabenzyl compounds MBn4 (M = Zr, Ti), upon protonolysis with an equimolar amount of the tetradentate amine-tris(phenol) ligand N[(2,4-tBu2C6H2(CH2)OH]3 in toluene from −30 to 25 °C, unexpectedly lead to amine-bis(phenoxy) dibenzyl complexes, BnCH2N[(2,4-tBu2C6H2(CH2)O]2MBn2 (M = Zr (1), Ti (2)) in 80% (1) and 75% (2) yields. This reaction involves an apparent cleavage of the >NCH2–ArOH bond (loss of the phenol in the ligand) and formation of the >NCH2–CH2Bn bond (gain of the benzyl group in the ligand). Structural characterization of 1 by X-ray diffraction analysis confirms that the complex formed is a bis(benzyl) complex of Zr coordinated by a newly derived tridentate amine-bis(phenoxy) ligand arranged in a mer configuration in the solid state. The abstractive activation of 1 and 2 with B(C6F5)3·THF in CD2Cl2 at room temperature generates the corresponding benzyl cations {BnCH2N[(2,4-tBu2C6H2(CH2)O]2MBn(THF)}+[BnB(C6F5)3]− (M = Zr (3), Ti, (4)). These cationic complexes, along with their analogues derived from (imino)phenoxy tri- and dibenzyl complexes, [(2,6-iPr2C6H3)N═C(3,5-tBu2C6H2)O]ZrBn3 (5) and [2,4-Br2C6H2(O)(6-CH2(NC5H9))CH2N═CH(2-adamantyl-4-MeC6H2O)]ZrBn2 (6), have been found to effectively polymerize the biomass-derived renewable β-methyl-α-methylene-γ-butyrolactone (βMMBL) at room temperature into the highly stereoregular polymer PβMMBL with an isotacticity up to 99% mm. A combined experimental and DFT study has yielded a mechanistic pathway for the observed unusual C–C bond cleavage in the present protonolysis reaction between ZrBn4 and N[(2,4-tBu2C6H2(CH2)OH]3 for the formation of complex 1, which involves the benzyl radical and the Zr(III) species, resulting from thermal and photochemical decomposition of ZrBn4, followed by a series of reaction sequences consisting of protonolysis, tautomerization, H-transfer, oxidation, elimination, and radical coupling
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