16 research outputs found

    Women’s access to and control over land in the current land administration system in two rural kebeles in Ada’a Woreda of Oromia Region

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    The study is designed to explore the status of rural women in access to and control over land in the current land administration system in two rural Kebeles in East Shewa Zone Ada’a Woreda of Oromia region on smallholder farmers’ landholding registration. The Ormia National Regional State Rural Land Administration and Use Proclamation and its implementation procedure are examined from a gender perspective in terms of ensuring rural women’s land holding rights and control they have over land. Historical overview on the land question in Ethiopia revealed that tenure systems evolved through historical periods. Land remained under men’s control throughout history and men’s control over land was strengthened by the rural land reform carried out by the Derg. This tenure reform applied rural land distribution using households as unit for rural land allocation and women were disadvantaged as most rural households were headed by men. The Oromia rural land proclamation is not discriminatory on basis of sex. However, policy gaps are evident in addressing women specific issues such as issues of FHHs and women under polygamous marriages. Gaps also exist between policy and implementation. Customary laws and practices have serious impacts on women’s land rights at the level of implementation. The research applied both quantitative and qualitative methods in view of feminist research methodology to properly address issues from a gender perspective. Survey of 318 households was conducted administering questionnaires in the quantitative method. The qualitative method applied was interviews with relevant Woreda office and Kebele LACs, focus group discussions with rural women, case stories and observation. Triangulation method is applied in data collection, data presentation and in analysis of findings. Study findings reveal that women’s access rights to land is less equal than legally provided. This study evidences gaps between policy and implementation. Customary laws and traditional practices generally have impacts on land access rights of single/unmarried, divorced, widowed women and on access rights of women in polygamous marriages. Women’s control over land is not efficiently addressed by the regional rural land policy. This is a significant policy drawback as women’s equal rights on land could not be achieved without gaining control over land. The land administration system in general and the land registration process in particular has not considered women’s participation in community activities and decision-making. Women are not represented in LACs and Sub-Committees in both Kebeles. Study findings indicate absence of autonomous institution as gap in addressing women’s issues in the land administration system. This study also revealed loose linkages between the rural land policy and other regional legislations like the regional family law which provides women’s equal rights on land in marriage and on its abandonment. This study forwards recommendation to address gender gaps identified to ensure women’s equal access to and control over land in the study area. The Oromia rural land proclamation needs revision from a gender perspective to address women’s specific issues and the land administration system should consider women’s participation in the process, their contribution to the system as well as their equal benefits from policy outcomes

    Direct Simulation of Early-Stage Sec-Facilitated Protein Translocation

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    Direct simulations reveal key mechanistic features of early-stage protein translocation and membrane integration via the Sec-translocon channel. We present a novel computational protocol that combines non-equilibrium growth of the nascent protein with microsecond timescale molecular dynamics trajectories. Analysis of multiple, long timescale simulations elucidates molecular features of protein insertion into the translocon, including signal-peptide docking at the translocon lateral gate (LG), large lengthscale conformational rearrangement of the translocon LG helices, and partial membrane integration of hydrophobic nascent-protein sequences. Furthermore, the simulations demonstrate the role of specific molecular interactions in the regulation of protein secretion, membrane integration, and integral membrane protein topology. Salt-bridge contacts between the nascent-protein N-terminus, cytosolic translocon residues, and phospholipid head groups are shown to favor conformations of the nascent protein upon early-stage insertion that are consistent with the Type II (N<sub>cyt</sub>/C<sub>exo</sub>) integral membrane protein topology, and extended hydrophobic contacts between the nascent protein and the membrane lipid bilayer are shown to stabilize configurations that are consistent with the Type III (N<sub>exo</sub>/C<sub>cyt</sub>) topology. These results provide a detailed, mechanistic basis for understanding experimentally observed correlations between integral membrane protein topology, translocon mutagenesis, and nascent-protein sequence

    Position-Specific and Clumped Stable Isotope Studies: Comparison of the Urey and Path-Integral Approaches for Carbon Dioxide, Nitrous Oxide, Methane, and Propane

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    We combine path-integral Monte Carlo methods with high-quality potential energy surfaces to compute equilibrium isotope effects in a variety of systems relevant to ‘clumped’ isotope analysis and isotope geochemistry, including CO<sub>2</sub>, N<sub>2</sub>O, methane, and propane. Through a systematic study of heavy-atom isotope-exchange reactions, we quantify and analyze errors that arise in the widely used Urey model for predicting equilibrium constants of isotope-exchange reactions using reduced partition function ratios. These results illustrate that the Urey model relies on a nontrivial cancellation of errors that can shift the apparent equilibrium temperature by as much as 35 K for a given distribution of isotopologues. The calculations reported here provide the same level of precision as the best existing analytical instrumentation, resolving the relative enrichment of certain isotopologues to as little as 0.01‰. These findings demonstrate path-integral methods to be a rigorous and viable alternative to more approximate methods for heavy-atom geochemical applications

    Transferability in Machine Learning for Electronic Structure via the Molecular Orbital Basis

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    We present a machine learning (ML) method for predicting electronic structure correlation energies using Hartree–Fock input. The total correlation energy is expressed in terms of individual and pair contributions from occupied molecular orbitals, and Gaussian process regression is used to predict these contributions from a feature set that is based on molecular orbital properties, such as Fock, Coulomb, and exchange matrix elements. With the aim of maximizing transferability across chemical systems and compactness of the feature set, we avoid the usual specification of ML features in terms of atom- or geometry-specific information, such atom/element-types, bond-types, or local molecular structure. ML predictions of MP2 and CCSD energies are presented for a range of systems, demonstrating that the method maintains accuracy while providing transferability both within and across chemical families; this includes predictions for molecules with atom-types and elements that are not included in the training set. The method holds promise both in its current form and as a proof-of-principle for the use of ML in the design of generalized density-matrix functionals

    Enhancing Cation Diffusion and Suppressing Anion Diffusion via Lewis-Acidic Polymer Electrolytes

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    Solid polymer electrolytes (SPEs) have the potential to increase both the energy density and stability of lithium-based batteries, but low Li<sup>+</sup> conductivity remains a barrier to technological viability. SPEs are designed to maximize Li<sup>+</sup> diffusivity relative to the anion while maintaining sufficient salt solubility. It is thus remarkable that poly­(ethylene oxide) (PEO), the most widely used SPE, exhibits Li<sup>+</sup> diffusivity that is an order of magnitude smaller than that of typical counterions at moderate salt concentrations. We show that Lewis-basic polymers like PEO favor slow cation and rapid anion diffusion, while this relationship can be reversed in Lewis-acidic polymers. Using molecular dynamics, polyboranes are identified that achieve up to 10-fold increases in Li<sup>+</sup> diffusivities and significant decreases in anion diffusivities, relative to PEO in the dilute-ion regime. These results illustrate a general principle for increasing Li<sup>+</sup> diffusivity and transference number with chemistries that exhibit weaker cation and stronger anion coordination

    Molecular Seesaw: How Increased Hydrogen Bonding Can Hinder Excited-State Proton Transfer

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    A previously unexplained effect in the relative rate of excited-state intramolecular proton transfer (ESIPT) in related indole derivatives is investigated using both theory and experiment. Ultrafast spectroscopy [<i>J. Phys. Chem. A</i>, <b>2015</b>, <i>119</i>, 5618–5625] found that although the diol 1,3-bis­(2-pyridylimino)-4,7-dihydroxy­isoindole exhibits two equivalent intramolecular hydrogen bonds, the ESIPT rate associated with tautomerization of either hydrogen bond is a factor of 2 slower than that of the single intramolecular hydrogen bond in the ethoxy-ol 1,3-bis­(2-pyridylimino)-4-ethoxy-7-hydroxy­isoindole. Excited-state electronic structure calculations suggest a resolution to this puzzle by revealing a seesaw effect in which the two hydrogen bonds of the diol are both longer than the single hydrogen bond in the ethoxy-ol. Semiclassical rate theory recovers the previously unexplained trends and leads to clear predictions regarding the relative H/D kinetic isotope effect (KIE) for ESIPT in the two systems. The theoretical KIE predictions are tested using ultrafast spectroscopy, confirming the seesaw effect

    Embedded Mean-Field Theory

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    We introduce embedded mean-field theory (EMFT), an approach that flexibly allows for the embedding of one mean-field theory in another without the need to specify or fix the number of particles in each subsystem. EMFT is simple, is well-defined without recourse to parameters, and inherits the simple gradient theory of the parent mean-field theories. In this paper, we report extensive benchmarking of EMFT for the case where the subsystems are treated using different levels of Kohn–Sham theory, using PBE or B3LYP/6-31G* in the high-level subsystem and LDA/STO-3G in the low-level subsystem; we also investigate different levels of density fitting in the two subsystems. Over a wide range of chemical problems, we find EMFT to perform accurately and stably, smoothly converging to the high-level of theory as the active subsystem becomes larger. In most cases, the performance is at least as good as that of ONIOM, but the advantages of EMFT are highlighted by examples that involve partitions across multiple bonds or through aromatic systems and by examples that involve more complicated electronic structure. EMFT is simple and parameter free, and based on the tests provided here, it offers an appealing new approach to a multiscale electronic structure

    2D THz-THz-Raman Photon-Echo Spectroscopy of Molecular Vibrations in Liquid Bromoform

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    Fundamental properties of molecular liquids are governed by long-range interactions that most prominently manifest at terahertz (THz) frequencies. Here we report the detection of nonlinear THz photon-echo (rephasing) signals in liquid bromoform using THz-THz-Raman spectroscopy. Together, the many observed signatures span frequencies from 0.5 to 8.5 THz and result from couplings between thermally populated ladders of vibrational states. The strongest peaks in the spectrum are found to be multiquantum dipole and 1-quantum polarizability transitions and may arise from nonlinearities in the intramolecular dipole moment surface driven by intermolecular interactions

    Breaking the Correlation between Energy Costs and Kinetic Barriers in Hydrogen Evolution via a Cobalt Pyridine-Diimine-Dioxime Catalyst

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    A central challenge in the development of inorganic hydrogen evolution catalysts is to avoid deleterious coupling between the energetics of metal site reduction and the kinetics of metal hydride formation. In this work, we combine theoretical and experimental methods to investigate cobalt diimine-dioxime catalysts that show promise for achieving this aim by introducing an intramolecular proton shuttle via a pyridyl pendant group. Using over 200 coupled-cluster-level electronic structure calculations of the Co-based catalyst with a variety of pyridyl substituents, the energetic and kinetic barriers to hydrogen formation are investigated, revealing nearly complete decoupling of the energetics of Co reduction and the kinetics of intramolecular Co hydride formation. These calculations employ recently developed quantum embedding methods that allow for local regions of a molecule to be described using high-accuracy wavefunction methods (such as CCSD­(T)), thus overcoming significant errors in the DFT-level description of transition-metal complexes. Experimental synthesis and cyclic voltammetry of the methyl-substituted form of the catalyst indicate that protonation of the pendant group leaves the Co reduction potential unchanged, which is consistent with the theoretical prediction that these catalysts can successfully decouple the electronic structures of the transition-metal and ligand-protonation sites. Additional computational analysis indicates that introduction of the pyridyl pendant group enhances the favorability of intramolecular proton shuttling in these catalysts by significantly reducing the energetic barrier for metal hydride formation relative to previously studied cobalt diimine-dioxime catalysts. These results demonstrate a promising proof of principle for achieving uncoupled and locally tunable intramolecular charge-transfer events in the context of homogeneous transition-metal catalysts

    Globally Suppressed Dynamics in Ion-Doped Polymers

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    We investigate how ion–polymer complexation suppresses molecular motion in conventional polymer electrolytes using molecular dynamics (MD) simulations of lithium hexafluorophosphate in poly­(ethylene oxide) and a modified Rouse model. The employed model utilizes an inhomogeneous friction distribution to describe ion–polymer interactions and provides an effective way to examine how ion–polymer interactions affect polymer motion. By characterizing the subdiffusive Li<sup>+</sup> transport and polymer relaxation times at several salt concentrations, we observe that increases in local friction due to ion-polymer complexation are significantly smaller than previously assumed. We find that a Rouse-based model that only considers local increases in friction cannot simultaneously capture the magnitude of increased polymer relaxation times and the apparent power-law exponent for Li<sup>+</sup> subdiffusion observed in MD simulations. This incompatibility is reconciled by augmenting the modified Rouse model with a term that increases the global friction with the square of the salt concentration; this significantly improves the agreement between the model and MD, indicating the importance of ion–ion interactions and distributions on ion/polymer mobility