Relative notions of flatness are introduced as a mean to gauge the extent of the flatness of any given module. Every module is thus endowed with a flatness domain and, for every ring, the collection of flatness domains of all of its modules is a lattice with respect to class inclusion. This lattice, the flatness profile of the ring, allows us, in particular, to focus on modules which have a smallest flatness domain (namely, one consisting of all regular modules.) We establish that such modules exist over arbitrary rings and we call them Rugged Modules. Rings all of whose (cyclic) modules are rugged are shown to be precisely the von Neumann regular rings. We consider rings without a flatness middle class (i.e., rings for which modules must be either flat or rugged.) We obtain that, over a right Noetherian ring every left module is rugged or flat if and only if every right module is poor or injective if and only if R = S×T, where S is semisimple Artinian and T is either Morita equivalent to a right PCI-domain, or T is right Artinian whose Jacobson radical properly contains no nonzero ideals. Character modules serve to bridge results about flatness and injectivity profiles; in particular, connections between rugged and poor modules are explored. If R is a ring whose regular left modules are semisimple, then a right module M is rugged if and only if its character left module M+ is poor. Rugged Abelian groups are fully characterized and shown to coincide precisely with injectively poor and projectively poor Abelian groups. Also, in order to get a feel for the class of rugged modules over an arbitrary ring, we consider the homological ubiquity of rugged modules in the category of all modules in terms of the feasibility of rugged precovers and covers for arbitrary modules. 相似文献
The high‐speed synchrotron X‐ray imaging technique was synchronized with a custom‐built laser‐melting setup to capture the dynamics of laser powder‐bed fusion processes in situ. Various significant phenomena, including vapor‐depression and melt‐pool dynamics and powder‐spatter ejection, were captured with high spatial and temporal resolution. Imaging frame rates of up to 10 MHz were used to capture the rapid changes in these highly dynamic phenomena. At the same time, relatively slow frame rates were employed to capture large‐scale changes during the process. This experimental platform will be vital in the further understanding of laser additive manufacturing processes and will be particularly helpful in guiding efforts to reduce or eliminate microstructural defects in additively manufactured parts. 相似文献
Tritium (3H) is an essential tracer of the Earth's water cycle; yet widespread adoption of tritium in hydrologic studies remains a challenge because of analytical barriers to quantification and detection of 3H by electrolytic pre-concentration. Here, we propose a simple tritium electrolytic enrichment system based on the use of solid polymer electrolyte membranes (PEMs) that can be used to enrich 3H in 250–3000?mL environmental water samples to a 10-mL final volume. The IAEA PEM-3H system reported here can produce high enrichment factors (>70-fold) and, importantly, removes some of the deterrents to conventional 3H enrichments methods, including the use of toxic electrolysis and neutralization chemicals, spike standards, a complex electrolysis apparatus that requires extensive cooling and temperature controls, and improves precision by eliminating the need for tracking recovery gravimetrics. Preliminary results with varying operating conditions show 3H enrichments to 70-fold and higher are feasible, spanning a wide range of tritium activities from 5 to 150 TU with a precision of ～4.5?%. Further work is needed to quantify inter-sample memory and to establish lower 3H detection limits. The IAEA PEM-3H system is open source, with 3-D CAD and design files made freely available for adoption and improvement by others. 相似文献
We present terminal deoxynucleotidyl transferase-catalyzed enzymatic polymerization (TcEP) for the template-free synthesis of high-molecular-weight, single-stranded DNA (ssDNA) and demonstrate that it proceeds by a living chain-growth polycondensation mechanism. We show that the molecular weight of the reaction products is nearly monodisperse, and can be manipulated by the feed ratio of nucleotide (monomer) to oligonucleotide (initiator), as typically observed for living polymerization reactions. Understanding the synthesis mechanism and the reaction kinetics enables the rational, template-free synthesis of ssDNA that can be used for a range of biomedical and nanotechnology applications. 相似文献
The synthesis of poly(acrylic acid) (PAA) of low molar mass under safe conditions is difficult due to the high polymerization rate of acrylic acid (AA) and the fast heat generation. The aqueous‐solution “semibatch” polymerization of non‐ionized AA in almost starved conditions involves high initiator loads when low molar masses are required. This article proposes the simultaneous feeding of AA and nonconventional chain transfer agents (CTA) as a strategy aimed at controlling both the molar masses and the generated heat rate. Three CTAs are investigated: 2‐mercaptoethanol, thioglycolic acid, and isopropyl alcohol. Even when PAA of relatively low molar mass can be produced by adequately selecting the flow rates and concentrations of both AA and CTA, it is found that the nature of CTA can have a significant effect on the polymerizations kinetics. The mechanisms responsible for these effects are discussed with the help of a representative mathematical model.
Latex emulsions depend strongly on the polymer composition, and particle size distribution, which in turn, is a function of the preparation of the latex and on the formulation and composition variables. This study reports measurements of particle size and particle size distribution of latex emulsions as function of the reaction time and the type and concentration of emulsifier by using the multiwavelength spectroscopy technique. Results show changes in the particle size of latex emulsions with the reaction time, obtaining larger particles and broader distributions with increasing of Tween 80 ratio. The steric stabilization provides the sole nonionic emulsifier is not enough to protect the polymer particle, causing the flocculation among the interactive particles, resulting in unstable latex. However, latex emulsions prepared with Tween 80 ratio <70 wt.% can stabilize efficiently the nucleated particles, probably due to the effects provided by both, the electrostatic and steric stabilization mechanisms. The same effect is shown in the curves of conversion (%) as a function of reaction time, resulting in slower polymerization rate for Tween 80 ratio >70 wt.%. On the other hand, smaller polymer particles, in all range of emulsifier mixture, have been obtained to higher emulsifier concentration. 相似文献
The M@C36 compounds form a family of small endohedral metallofullerenes. Recently, these have been detected as the smallest endohedral compounds formed with Sc, Y, and La. For the first time, these compounds are studied theoretically. Calculations obtained at the dispersion‐corrected DFT level PBE‐D3(BJ)/def2‐TZVP agree admirably with experimental results. The zero‐point energy corrected binding energies can explain the lower abundance of La@C36 in comparison with Sc@C36 and Y@C36. Their small HOMO‐LUMO gaps denote high reactivity. The bond between Y and Sc with the cage is mostly covalent. In contrast, La is located at the fullerene's center with an ionic interaction; all metals transferred charge to the cage. Furthermore, La@C36 was found in doublet state and the others preferred the quartet state. To conclude, according to the analysis of aromaticity performed by the NICS(0)iso index, the insertion of none of these metals increase the aromaticity. 相似文献
In a recent article, Y. Liu, X. Cheng, H. Cheng, J. Cheng and X. Song [Mol. Phys., 114:19, 2817–2823] report on the calculation of potential energy curves and the derivation of spectroscopic constants and line intensities for the lowest energy electronic states of HCl+. There are several shortcomings in the article; the most notable being the incorrect ordering of the 2П3/2 and 2П1/2 state energies, erroneous selection rules, which lead to the absence of a Q-branch in their predicted spectra, incorrect Höln–London factors, and a missing appendix. 相似文献
The main goal of this work is to adapt a Physics problem to the Machine Learning (ML) domain and to compare several techniques to solve it. The problem consists of how to perform muon count from the signal registered by particle detectors which record a mix of electromagnetic and muonic signals. Finding a good solution could be a building block on future experiments. After proposing an approach to solve the problem, the experiments show a performance comparison of some popular ML models using two different hadronic models for the test data. The results show that the problem is suitable to be solved using ML as well as how critical the feature selection stage is regarding precision and model complexity. 相似文献
