Multiscale Expression Of Apatite Dissolution

The weathering of apatite is the foundation of the phosphorus cycle and essential to life, yet little is known about the nanoscale mechanisms driving apatite weathering. Deciphering nanoscale dissolution in apatite is a significant step to understand phosphate weathering behavior, that was key to the development of life. Determining what controls apatite weathering can impact many areas of environmental and medical mineralogy such as dentistry, contaminant scavenging, geochronology, and paleoenvironment studies. The aim of this study was to characterize apatite dissolution across scales with an emphasis on the nanoscale mechanisms. Recent research on the weathering of silicate minerals at the nanoscale has provided telling evidence of a relatively new chemical weathering model referred to as coupled interfacial dissolution-precipitation (CIDR) mechanism. We hypothesize that this mechanism could be broadened to phosphate minerals. To investigate crystals of Durango fluorapatite (FAP) and hydroxyl-chlorapatite (HAP) were hydrolyzed in flow-through devices with pH 3 HNO3 solutions. Apatites used in the study were chemically and structurally characterized via Single Crystal-XRD, with particular emphasis on the anion composition and atomic arrangement. Determination of the mechanisms of dissolution was carried at multiple scales using ICP-OES chemical analysis (macroscale), SEM (microscale) and STEM-HAADF-EDS/EELS on FIB liftouts (nanoscale). At the macroscale, The anionic composition of the apatite controlled its weathering rate. As expected, HAP dissolution occurred at faster rates compared to FAP. SEM characterization of the crystal surfaces pre- and post-dissolution revealed the development of etch pits during dissolution, however, more pronounced for FAP than HAP. Observation of the mineral/solution interface at the nanoscale using STEM-HAADF revealed the development of a nanometric amorphous layer likely depleted in Ca compared to P. The observation of a sharp crystalline/amorphous transition and 5 to 15 nanometers thick amorphous surface altered layer, associated with a depletion in Ca suggests that similar to silicate, apatite is subject to a coupled interfacial dissolution-reprecipitation mechanism. This potential discovery could transform our understanding of phosphate behavior in medical and environmental mineralogy fields

Does Misclassifying Non-confounding Covariates as Confounders Affect the Causal Inference within the Potential Outcomes Framework?

The Potential Outcome Framework (POF) plays a prominent role in the field of causal inference. Most causal inference models based on the POF (CIMs-POF) are designed for eliminating confounding bias and default to an underlying assumption of Confounding Covariates. This assumption posits that the covariates consist solely of confounders. However, the assumption of Confounding Covariates is challenging to maintain in practice, particularly when dealing with high-dimensional covariates. While certain methods have been proposed to differentiate the distinct components of covariates prior to conducting causal inference, the consequences of treating non-confounding covariates as confounders remain unclear. This ambiguity poses a potential risk when conducting causal inference in practical scenarios. In this paper, we present a unified graphical framework for the CIMs-POF, which greatly enhances the comprehension of these models' underlying principles. Using this graphical framework, we quantitatively analyze the extent to which the inference performance of CIMs-POF is influenced when incorporating various types of non-confounding covariates, such as instrumental variables, mediators, colliders, and adjustment variables. The key findings are: in the task of eliminating confounding bias, the optimal scenario is for the covariates to exclusively encompass confounders; in the subsequent task of inferring counterfactual outcomes, the adjustment variables contribute to more accurate inferences. Furthermore, extensive experiments conducted on synthetic datasets consistently validate these theoretical conclusions.Comment: 12 pages, 4 figure

Femtocell Performance Over Non-SLA xDSL Access Network

Environmental medicin

Optimization of the structure of TTR Ligands for Half-life Extension (TLHE)

Many potential therapeutic agents face challenges for their clinical development due to short circulation half-life. As a result, prolonging the half-life of therapeutic drugs in circulation while preserving their hydrophilicity and small size will be a key step toward more effective and safe pharmacological molecules. Our lab developed a new approach for enhancing the safety and efficacy of therapeutic agents. By endowing therapeutic agents with a hydrophilic small molecule (a derivative of the clinical candidate, AG10) which reversibly binds to the serum protein transthyretin (TTR), the half-life of the therapeutic agent should be extended by binding to the TTR in serum. We termed this technology TTR Ligand for half-life extension (TLHEs). The approach involved using TLHE, which binds with TTR by high specificity and affinity. Our group has already shown that this technology extends the half-life of peptides, small molecules, and proteins without seriously affecting their binding activity towards their receptor and efficacy. As we are expanding the applicability of TLHE to extend the half-life of hydrophobic moieties, increasing the polarity of the TLHE linker could be beneficial to maintain overall hydrophilicity. Our main objective here is to see the effect of TTR binding affinity and selectivity of TLHE in serum when we attach a hydrophilic glutamic acid in the TLHE linker

Nanoscale simulation of crystal defects with application to mantle minerals

Minor and trace elements can influence the chemical and physical properties of the Earth's mantle, whether by forming separate minerals that can host trace elements at far higher concentrations than major mantle minerals, or by influencing physical properties of major minerals, for instance by enhancing diffusion or pinning topological defects. The present study uses atomistic computational modeling to investigate the properties of calcium phosphate minerals at mantle pressures, and to determine if cation vacancies can lubricate dislocation glide in mantle minerals. With their large, high-coordination cation sites, calcium phosphate minerals can potentially dissolve large quantities of incompatible elements, and may be an important mantle reservoirs for these elements. Quantum mechanical calculations are used to determine the variation of structure and properties of apatite, a common low-pressure phosphate, with the identity of its channel anion. The crystal structure and compressibility are both found to vary substantially with channel anion identity. Tuite, which forms by the breakdown of apatite at high pressure, may extend the phosphorous cycle beyond the stability field of apatite and into the lower mantle. DFT calculations are used to show that the pressure at which apatite decomposes to form tuite is sensitive to the identity of the channel anion. The calculated bulk moduli of the calcium-hosting sites in tuite are considerably lower than those of the M site in CaSiO3 perovskite (cpv). Atomistic calculations show that strontium and barium impurities partition strongly from cpv into tuite. The second part of this thesis considers the role that dislocations play in hosting vacancy-related defects, and influence that these segregated defects may have on the rheology of mantle minerals. Interatomic potentials are used to calculate energies for the segregation of bare and protonated cation defects to dislocation cores in MgO and forsterite. Vacancies segregate strongly to [100](010) and [001](010) dislocations in forsterite. [100](010) edge dislocations serve as particularly suitable hosts for vacancies on the M1 sub-lattice, while vacant M2 sites, which are energetically unfavorable in the unstrained bulk lattice are more common around [001](010) edge dislocations. Similarly, both {□Mg}″ and {2HMg}X defects segregate strongly to all of the major dislocation slip systems in MgO. For both minerals, cation vacancies will be far higher at dislocation core sites than in the unstrained lattice. Peierls-Nabarro calculations, parameterized using generalized stacking fault energies calculated using plane-wave density functional theory, show that protonated vacancies increase dislocation core widths and reduce the Peierls stresses in MgO. Bare Mg vacancies, especially those on the M2 sub-lattice, similarly reduce g-line energies and Peierls stresses for the dislocations in olivine. The magnitude of this decrease depends strongly on dislocation and the type of the lattice site (i.e. M1 or M2). Concentrations of vacancy related defects are likely to be elevated particularly in mantle wedge, due to the combination of oxidizing conditions and the availability of liquid water from dehydrating phases in the subducting slab, and changes in the olivine deformation fabric in these regions match those predicted in this study

Pathway to a fully data-driven geotechnics: lessons from materials informatics

This paper elucidates the challenges and opportunities inherent in integrating data-driven methodologies into geotechnics, drawing inspiration from the success of materials informatics. Highlighting the intricacies of soil complexity, heterogeneity, and the lack of comprehensive data, the discussion underscores the pressing need for community-driven database initiatives and open science movements. By leveraging the transformative power of deep learning, particularly in feature extraction from high-dimensional data and the potential of transfer learning, we envision a paradigm shift towards a more collaborative and innovative geotechnics field. The paper concludes with a forward-looking stance, emphasizing the revolutionary potential brought about by advanced computational tools like large language models in reshaping geotechnics informatics

Interference mitigation in cognitive femtocell networks

“A thesis submitted to the University of Bedfordshire, in partial fulfilment of the requirements for the degree of Doctor of Philosophy”.Femtocells have been introduced as a solution to poor indoor coverage in cellular communication which has hugely attracted network operators and stakeholders. However, femtocells are designed to co-exist alongside macrocells providing improved spatial frequency reuse and higher spectrum efficiency to name a few. Therefore, when deployed in the two-tier architecture with macrocells, it is necessary to mitigate the inherent co-tier and cross-tier interference. The integration of cognitive radio (CR) in femtocells introduces the ability of femtocells to dynamically adapt to varying network conditions through learning and reasoning. This research work focuses on the exploitation of cognitive radio in femtocells to mitigate the mutual interference caused in the two-tier architecture. The research work presents original contributions in mitigating interference in femtocells by introducing practical approaches which comprises a power control scheme where femtocells adaptively controls its transmit power levels to reduce the interference it causes in a network. This is especially useful since femtocells are user deployed as this seeks to mitigate interference based on their blind placement in an indoor environment. Hybrid interference mitigation schemes which combine power control and resource/scheduling are also implemented. In a joint threshold power based admittance and contention free resource allocation scheme, the mutual interference between a Femtocell Access Point (FAP) and close-by User Equipments (UE) is mitigated based on admittance. Also, a hybrid scheme where FAPs opportunistically use Resource Blocks (RB) of Macrocell User Equipments (MUE) based on its traffic load use is also employed. Simulation analysis present improvements when these schemes are applied with emphasis in Long Term Evolution (LTE) networks especially in terms of Signal to Interference plus Noise Ratio (SINR)

LKB1 as the ghostwriter of crypt history

Familial cancer syndromes present rare insights into malignant tumor development. The molecular background of polyp formation and the cancer prone state in Peutz-Jeghers syndrome remain enigmatic to this day. Previously, we proposed that Peutz-Jeghers polyps are not pre-malignant lesions, but an epiphenomenon to the malignant condition. However, Peutz-Jeghers polyp formation and the cancer-prone state must both be accounted for by the same molecular mechanism. Our contribution focuses on the histopathology of the characteristic Peutz-Jeghers polyp and recent research on stem cell dynamics and how these concepts relate to Peutz-Jeghers polyposis. We discuss a protracted clonal evolution scenario in Peutz-Jeghers syndrome due to a germline LKB1 mutation. Peutz-Jeghers polyp formation and malignant transformation are separately mediated through the same molecular mechanism played out on different timescales. Thus, a single mechanism accounts for the development of benign Peutz-Jeghers polyps and for malignant transformation in Peutz-Jeghers syndrome