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npj Computational Materials 2022年第1期8卷 757-766页

作者： Enze Chen artur tamm Tao Wang Mario E.Epler Mark Asta Timofey Frolov Department of Materials Science and Engineering University of CaliforniaBerkeleyCA94720USA Materials Sciences Division Lawrence Berkeley National LaboratoryBerkeleyCA94720USA Materials Science Division Lawrence Livermore National LaboratoryLivermoreCA94550USA Carpenter Technology Corporation PhiladelphiaPA19103USA

Antiphase boundaries(APBs)are planar defects that play a critical role in strengthening Ni-based superalloys,and their sensitivity to alloy composition offers a flexible tuning parameter for alloy ***,we report a computational workflow to enable the development of sufficient data to train machine-learning(ML)models to automate the study of the effect of composition on the(111)APB energy in Ni_(3)Al-based *** employ ML to leverage this wealth of data and identify several physical properties that are used to build predictive models for the APB energy that achieve a cross-validation error of 0.033 J m^(−2).We demonstrate the transferability of these models by predicting APB energies in commercial ***,our use of physically motivated features such as the ordering energy and stoichiometry-based features opens the way to using existing materials properties databases to guide superalloy design strategies to maximize the APB energy.

关键词： Ni_(3)Al alloy superalloy

Recovering 3D structural properties of galaxies from SDSS-like photometry

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Research in Astronomy and Astrophysics 2015年第10期15卷 1613-1628页

作者： Elmo Tempel Antti tamm Rain Kipper Teeter Tenjes Tartu Observatory Institute of Physics University of Tartu

Because of the 3D nature of galaxies, an algorithm for constructing spatial density distribution models of galaxies on the basis of galaxy images has many advan- tages over approximations of the surface density distribution. We present a method for deriving the spatial structure and overall parameters of galaxies from images and estimate its accuracy and derived parameter degeneracies on a sample of idealised model galaxies. The test galaxies consist component with varying proportions and of a disc-like component and a spheroidal properties. Both components are assumed to be axially symmetric and coplanar. We simulate these test galaxies as if they had been observed in the SDSS project through ugriz filters, thus gaining a set of realis- tically imperfect images of galaxies with known intrinsic properties. These artificial SDSS galaxies were thereafter remodelled by approximating the surface brightness distribution with a 2D projection of a bulge＋disc spatial distribution model and the restored parameters were compared to the initial ones. Down to the r-band limiting magnitude of 18, errors in the restored integral luminosities and colour indices re- main within 0.05 mag and errors in the luminosities of individual components within 0.2 mag. Accuracy of the restored bulge-to-disc luminosity ratio （B/D） is within 40% in most cases, and becomes worse for galaxies with low B/D, but the general balance between bulges and discs is not shifted systematically. Assuming that the intrinsic disc axial ratio is ≤ 0.3, then the inclination angles can be estimated with errors 〈 5° for most of the galaxies with B/D 〈 2 and with errors 〈 15° up to B/D = 6. Errors in the recovered sizes of the galactic components are below 10% in most cases. The axial ratios and the shape parameter N of Einasto＇s distribution （similar to the Sersic index） are relatively inaccurate, but can provide statistical estimates for large samples. In general, models of disc components are more accurate than

关键词： methods: numerical -- galaxies: general -- galaxies: photometry --galaxies: structure

Evidence for the polyphyly of Encoelia and Encoelioideae with reconsideration of respective families in Leotiomycetes

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Fungal Diversity 2017年第1期82卷 183-219页

作者： Kadri Pärtel Hans-Otto Baral Heidi tamm Kadri Põldmaa Institute of Ecology and Earth Sciences University of TartuLai 40EE-51005 TartuEstonia Mycological Collections Institute of Agricultural and Environmental SciencesEstonian University of Life SciencesTartuEstonia Blaihofstraße 42 72074 TübingenGermany

This study focuses on the genus Encoelia and the subfamily Encoelioideae in the morphologically and ecologically diverse *** 28S and 18S rDNA as well as tef1,rpb1 and rpb2 were sequenced for 70 *** analyses revealed Encoelia and Encoelioideae to be highly polyphyletic,with species distributed among eight major *** fascicularis and *** belonged to Sclerotiniaceae and were combined in a new genus,*** comprised *** and Dencoeliopsis johnstonii,both accepted in *** type of Encoelia,***,was closely related to species of Velutarina,Cenangiopsis and *** species together with members of Hemiphacidiaceae formed a clade conforming to the emended concept of Cenangiaceae,introduced *** resurrected family,Cordieritidaceae,comprised ***,*** and species of Ameghiniella,Cordierites,Diplocarpa and Ionomidotis,characterised by inamyloid asci and a positive ionomidotic *** glauca showed closest affinities with Chlorociboria species in Chlorociboriaceae.A new genus,Xeropilidium,with sporodochial and pycnidial synanamorphs,was described for the distinct encoelioid member of the Chaetomellaceae,previously known as *** and ecological synapomorphies were distinguished from convergent characters to delimit monophyletic taxa including encoelioid *** of public sequences from various biological samples in ITS rDNA analyses allowed identification of sequenced organisms at species,genus,or family level and added information on the ecology of seversal *** of Cenangiaceae appeared to be widespread as *** of encoelioid genera in Chaetomellaceae and Sclerotiniaceae added xylicolous saprotrophs to these families.

关键词： Environmental sequencing Fungicolous ascomycetes Helotiaceae Lichenicolous fungi Forest pathogens Taxonomy

Time’s Arrow in a Finite Universe

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International Journal of Astronomy and Astrophysics 2015年第2期5卷 70-78页

作者： Martin tamm Department of Mathematics University of Stockholm Stockholm Sweden

In this paper, a simple model for a closed multiverse as a finite probability space is analyzed. For each moment of time on a discrete time-scale, only a finite number of states are possible and hence each possible universe can be viewed as a path in a huge but finite graph. By considering very general statistical assumptions, essentially originating from Boltzmann, we make the set of all such paths (the multiverse) into a probability space, and argue that under certain assumptions, the probability for a monotonic behavior of the entropy is enormously much larger then for a behavior with low entropy at both ends. The methods used are just very simple combinatorial ones, but the conclusion suggests that we may live in a multiverse which from a global point of view is completely time-symmetric in the sense that universes with Time’s Arrow directed forwards and backwards are equally probable. However, for an observer confined to just one universe, time will still be asymmetric.

关键词： Multiverse Time’s Arrow Cosmology Entropy

Probabilistic Cosmology

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Journal of Modern Physics 2019年第12期10卷 1424-1438页

作者： Martin tamm Department of Mathematics University of Stockholm Stockholm Sweden

In this paper, an alternative approach to cosmology is discussed. Rather than starting from the field equations of general relativity, one can investigate the probability space of all possible universes and try to decide what kind of universe is the most probable one. Here two quite different models for this probability space are presented: the combinatorial model and the random curvature model. In addition, it is briefly discussed how these models could be applied to explain two fundamental problems of cosmology: Time’s Arrow and the accelerating expansion.

关键词： Cosmology Ensemble Time’s Arrow Accelerating Expansion Multiverse

Rotating Classical Strings

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Journal of Modern Physics 2017年第5期8卷 761-769页

作者： Martin tamm Department of Mathematics University of Stockholm Sweden

It is a starting point in string theory to assume that elementary particles are in fact rotating strings, and the final goal of the theory is a complete description of fundamental physics, including general relativity. This paper is instead concerned with the reversed question: starting from general relativity, is there a good way to motivate why rotating strings should be more natural models for elementary particles than, say, spherical particles or point-particles? Also, the purpose here is not to motivate full string theory. For example, no hidden dimensions come into play, only the four usual ones, and strings are defined in a very simple geometric way. Rather, the focus is on investigating an interesting mathematical property, which implies that strings may have special features with respect to rotation which spherically symmetric particles have not. In particular, it turns out that in a certain sense rotating strings are simpler than non-rotating ones. This is a consequence of the indefinite metric, and the main result states that the curvature of a non-rotating string, as measured by the square of the scalar curvature, may be reduced by letting it rotate in an appropriate way. The calculations underlying this theorem are heavy and have partly been car-ried out using Mathematica, although in principle the essential theorem may not require super-human labour.

关键词： General Relativity String Theory Rotation Curvature

On the Curvature of Rotating Objects

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Journal of Modern Physics 2015年第6期6卷 828-836页

作者： Martin tamm Department of Mathematics University of Stockholm Stockholm Sweden

In this paper, we investigate a certain property of curvature which differs in a remarkable way between Lorentz geometry and Euclidean geometry. In a certain sense, it turns out that rotating topological objects may have less curvature (as measured by integrating the square of the scalar curvature) than non-rotating ones. This is a consequence of the indefinite metric used in relativity theory. The results in this paper are mainly based of computer computations, and so far there is no satisfactory underlying mathematical theory. Some open problems are presented.

关键词： Curvature Rotation General Relativity

Accelerating Expansion in a Closed Universe

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Journal of Modern Physics 2015年第3期6卷 239-251页

作者： Martin tamm Department of Mathematics University of Stockholm Stockholm Sweden

In this paper, I suggest a possible explanation for the accelerating expansion of the universe. This model does not require any dark energy or quintessence. Rather, the idea is to suggest a different view on the origin of general relativity. Since it is very difficult to say something in general, I will mainly restrict myself to the case of very low curvature. The question about the underlying reasons for the acceleration is also closely related to the question whether the universe is a finite or infinite. It is part of the purpose of this paper to argue that a phase of accelerating expansion may be very well compatible with the idea of a closed universe.

关键词： Dark Energy Theory Quintessence Modified Gravity General Relativity Accelerating Expansion Cosmological Constant

Imaging of benign and malignant cystic pancreatic lesions and a strategy for follow up

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World Journal of Radiology 2010年第9期2卷 345-353页

作者： Priya Bhosale Aparna Balachandran Eric tamm Department of Diagnostic Radiology University of Texas M.D.Anderson Cancer Center

Cystic lesions in a variety of organs are being increasingly recognized as an incidental finding on cross-sectional *** lesions can be benign,premalignant or *** these cystic lesions are small it can be difficult to characterize them ***,with appropriate clinical history and knowledge of typical imaging features of cystic pancreatic lesions this can enable accurate diagnosis and thus guide appropriate *** this review,we provide an overview of the most common types of cystic lesions and their appearance on computer tomography,magnetic resonance imaging and *** will also discuss the follow up and management strategies of these cystic lesions.

关键词： Cystic pancreatic lesions Follow up management Imaging

Pig Liver Esterase-catalyzed Hydrolysis of Three Diesters of meso-Bicyclic Dicarboxylic Acid and Three Tetraesters of Tetrahydrofuran -2,3,4,5-tetracarboxylic Acid

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Chemical Research in Chinese Universities 2000年第4期16卷 369-374页

作者： MA Guang-En and tamm Ch. (National Institutes of Pharmaceutical Research & Development, Beijing 102206, P. R. China Institut fur Organishe Chemie der Universitat Basel, CH-4056 Basel Switzerland) Univ Basel Inst Organ Chem CH-4056 Basel Switzerland Natl Inst Pharmaceut Res & Dev Beijing 102206 Peoples R China

Three diesters of exo- syn-meso-oxabicyclo (2, 2, 1 ) -hept- 5- ene- 2, 3- dicarboxylic acid and three tetraesters of tetrahydrofuran-2, 3, 4, 5-tetracarboxylic acid were synthesized and tested with enantioselective h... 详细信息

关键词： Oxabicyclo(2 2 1 )-hept-5-ene-2 3-dicarboxylic acid Tetrahydrofuran-2 3 4 5- tetracarboxylic acid Esterification Hydrolysis Pig liver esterase(PLE)