Magnetization of the oceanic crust: TRM or CRM?

A model was proposed in which chemical remanent magnetization (CRM) acquired within the first 20 Ma of crustal evolution may account for 80% of the bulk natural remanent magnetization (NRM) of older basalts. The CRM of the crust is acquired as the original thermoremanent magnetization (TRM) is lost through low temperature alteration. The CRM intensity and direction are controlled by the post-emplacement polarity history. This model explains several independent observations concerning the magnetization of the oceanic crust. The model accounts for amplitude and skewness discrepancies observed in both the intermediate wavelength satellite field and the short wavelength sea surface magnetic anomaly pattern. It also explains the decay of magnetization away from the spreading axis, and the enhanced magnetization of the Cretaceous Quiet Zones while predicting other systematic variations with age in the bulk magnetization of the oceanic crust. The model also explains discrepancies in the anomaly skewness parameter observed for anomalies of Cretaceous age. Further studies indicate varying rates of TRM decay in very young crust which depicts the advance of low temperature alteration through the magnetized layer

Studies of the marine crustal magnetization at intermediate wavelengths

The data can be filtered at intermediate wavelengths to provde a data set which complements the satellite fields of MAGSAT, TSS and GRM. The filtered marine data set provides a high resolution data set which is closer to the source bodies than satellite survey data. However, the GRM and TSS could provide the necessary resolution to match the filtered sea surface field. The added resolution determines the nature of crustal magnetizations which give rise to the intermediate wavelength field. It is found that remanent magnetization is an important component over the oceans. Crustal deformation and plate motions result in magnetization vectors which differ significantly from the present day field directions. Induced magnetization or GRM are important components over the oceanic plateaus and spreading centers

Studies on the Mating Behavior of the House Fly, Musca Domestica L.

Author Institution: Entomology Research Division, Agric, Res. Serv., U.S.D.A. Gainesville, Fla

Attention-deficit hyperactivity disorder symptoms and brain morphology:Addressing potential selection bias with inverse probability weighting

The goal of this study was to examine what happens to established associations between attention deficit hyperactivity disorder (ADHD) symptoms and cortical surface and thickness regions once we apply inverse probability of censoring weighting (IPCW) to address potential selection bias. Moreover, we illustrate how different factors that predict participation contribute to potential selection bias. Participants were 9- to 11-year-old children from the Generation R study (N = 2707). Cortical area and thickness were measured with magnetic resonance imaging (MRI) and ADHD symptoms with the Child Behavior Checklist. We examined how associations between ADHD symptoms and brain morphology change when we weight our sample back to either follow-up (ages 9–11), baseline (cohort at birth), or eligible (population of Rotterdam at time of recruitment). Weights were derived using IPCW or raking and missing predictors of participation used to estimate weights were imputed. Weighting analyses to baseline and eligible increased beta coefficients for the middle temporal gyrus surface area, as well as fusiform gyrus cortical thickness. Alternatively, the beta coefficient for the rostral anterior cingulate decreased. Removing one group of variables used for estimating weights resulted in the weighted regression coefficient moving closer to the unweighted regression coefficient. In addition, we found considerably different beta coefficients for most surface area regions and all thickness measures when we did not impute missing covariate data. Our findings highlight the importance of using inverse probability weighting (IPW) in the neuroimaging field, especially in the context of mental health-related research. We found that including all variables related to exposure-outcome in the IPW model and combining IPW with multiple imputations can help reduce bias. We encourage future psychiatric neuroimaging studies to define their target population, collect information on eligible but not included participants and use inverse probability of censoring weighting (IPCW) to reduce selection bias.</p

Attention-deficit hyperactivity disorder symptoms and brain morphology:Addressing potential selection bias with inverse probability weighting

The goal of this study was to examine what happens to established associations between attention deficit hyperactivity disorder (ADHD) symptoms and cortical surface and thickness regions once we apply inverse probability of censoring weighting (IPCW) to address potential selection bias. Moreover, we illustrate how different factors that predict participation contribute to potential selection bias. Participants were 9- to 11-year-old children from the Generation R study (N = 2707). Cortical area and thickness were measured with magnetic resonance imaging (MRI) and ADHD symptoms with the Child Behavior Checklist. We examined how associations between ADHD symptoms and brain morphology change when we weight our sample back to either follow-up (ages 9–11), baseline (cohort at birth), or eligible (population of Rotterdam at time of recruitment). Weights were derived using IPCW or raking and missing predictors of participation used to estimate weights were imputed. Weighting analyses to baseline and eligible increased beta coefficients for the middle temporal gyrus surface area, as well as fusiform gyrus cortical thickness. Alternatively, the beta coefficient for the rostral anterior cingulate decreased. Removing one group of variables used for estimating weights resulted in the weighted regression coefficient moving closer to the unweighted regression coefficient. In addition, we found considerably different beta coefficients for most surface area regions and all thickness measures when we did not impute missing covariate data. Our findings highlight the importance of using inverse probability weighting (IPW) in the neuroimaging field, especially in the context of mental health-related research. We found that including all variables related to exposure-outcome in the IPW model and combining IPW with multiple imputations can help reduce bias. We encourage future psychiatric neuroimaging studies to define their target population, collect information on eligible but not included participants and use inverse probability of censoring weighting (IPCW) to reduce selection bias.</p

Invited Commentary:Conducting and Emulating Trials to Study Effects of Social Interventions

All else being equal, if we had 1 causal effect we wished to estimate, we would conduct a randomized trial with a protocol that mapped onto that causal question, or we would attempt to emulate that target trial with observational data. However, studying the social determinants of health often means there are not just 1 but several causal contrasts of simultaneous interest and importance, and each of these related but distinct causal questions may have varying degrees of feasibility in conducting trials. With this in mind, we discuss challenges and opportunities that arise when conducting and emulating such trials. We describe designing trials with the simultaneous goals of estimating the intention-to-treat effect, the per-protocol effect, effects of alternative protocols or joint interventions, effects within subgroups, and effects under interference, and we describe ways to make the most of all feasible randomized trials and emulated trials using observational data. Our comments are grounded in the study results of Courtin et al. (Am J Epidemiol. 2022;191(8):1444–1452)

An Ultra-Precise System for Electrical Resistivity Tomography Measurements

The objective of this research was to determine the feasibility of building and operating an ERT system that will allow measurement precision that is an order of magnitude better than existing systems on the market today and in particular if this can be done without significantly greater manufacturing or operating costs than existing commercial systems. Under this proposal, we performed an estimation of measurement errors in galvanic resistivity data that arise as a consequence of the type of electrode material used to make the measurements. In our laboratory, measurement errors for both magnitude and induced polarization (IP) were estimated using the reciprocity of data from an array of electrodes as might be used for electrical resistance tomography using 14 different metals as well as one non-metal - carbon. In a second phase of this study, using archival data from two long-term ERT surveys, we examined long-term survivability of electrodes over periods of several years. The survey sites were: the Drift Scale Test at Yucca Mountain, Nevada (which was sponsored by the U. S. Department of Energy as part of the civilian radioactive waste management program), and a water infiltration test at a site adjacent to the New Mexico Institute of Mines and Technology in Socorro, New Mexico (sponsored by the Sandia/Tech vadose program). This enabled us to compare recent values with historical values and determine electrode performance over the long-term as well as the percentage of electrodes that have failed entirely. We have constructed a prototype receiver system, made modifications and revised the receiver design. The revised prototype uses a new 24 bit analog to digital converter from Linear Technologies with amplifier chips from Texas Instruments. The input impedance of the system will be increased from 107 Ohms to approximately 1010 Ohms. The input noise level of the system has been decreased to approximately 10 Nanovolts and system resolution to about 1 Nanovolt at the highest gain range of 125 to 1. The receiver also uses very high precision and high temperature stability components. The goal is to improve the accuracy to better than 0.1%. The system has more receiver channels, eight, to allow efficient data collection at lower base frequencies. We are also implementing a frequency-domain acquisition mode in addition to the time-domain acquisition mode used in the earlier systems. Initial field tests were started in the fall of 2008. We conducted tests on a number of types of cable commonly used for resistivity surveys. A series of different tests were designed to determine if the couplings were primarily resistive, capacitive, or inductive in nature and to ascertain that the response was due to the cable cross-talk and did not depend on the receiver electronics. The results show that the problem appears to be primarily capacitive in nature and does not appear to be due to problems in the receiver electronics. Thus a great deal of emphasis has been placed on finding appropriate cables as well as stable electrodes that have low contact impedance at the very low current flows observed at the receiver. One of the issues in survey design and data collection has been determining how long one must wait before using the same electrode as a transmitter and as a receiver. A series of tests was completed in the laboratory sand tank where four-electrode measurements were made using the same dipole transmitters and dipole receivers (the dipoles used adjacent electrodes). For each data series, a single set of normal measurements were collected with no reciprocals and electrodes were never reused as a receiver after being used as a transmitter. After waiting a specified length of time, the reciprocal measurements were collected using a schedule of measurements. The order of this second schedule was rearranged such that if this second set of measurements were performed without first using the normal schedule, no electrode would be used as a receiver after being used as a transmitter. For this study, we cannot conclude that increasing the wait time increased or decreased the reciprocal errors, only that there was not a dramatic change in results with different wait times. Another issue in ERT data collection is the potential for the transmitter as well as the receiver end of an ERT system to create problems with reciprocity readings. Existing ERT systems typically use a constant voltage source. For the transmitter dipole, a constant voltage source has low output impedance, whereas a constant current source has high output impedance. Therefore, we devised an experiment to determine if a constant current source transmitter might produce smaller errors than a constant voltage source. These preliminary results suggest there is little or no difference in either resistivity or chargeability reciprocal errors using a constant voltage or constant current dipole drive source

Limitations of variable number of tandem repeat typing identified through whole genome sequencing of Mycobacterium avium subsp. paratuberculosis on a national and herd level

Background: Mycobacterium avium subsp. paratuberculosis (MAP), the causative bacterium of Johne’s disease in dairy cattle, is widespread in the Canadian dairy industry and has significant economic and animal welfare implications. An understanding of the population dynamics of MAP can be used to identify introduction events, improve control efforts and target transmission pathways, although this requires an adequate understanding of MAP diversity and distribution between herds and across the country. Whole genome sequencing (WGS) offers a detailed assessment of the SNP-level diversity and genetic relationship of isolates, whereas several molecular typing techniques used to investigate the molecular epidemiology of MAP, such as variable number of tandem repeat (VNTR) typing, target relatively unstable repetitive elements in the genome that may be too unpredictable to draw accurate conclusions. The objective of this study was to evaluate the diversity of bovine MAP isolates in Canadian dairy herds using WGS and then determine if VNTR typing can distinguish truly related and unrelated isolates.&lt;p&gt;&lt;/p&gt; Results: Phylogenetic analysis based on 3,039 SNPs identified through WGS of 124 MAP isolates identified eight genetically distinct subtypes in dairy herds from seven Canadian provinces, with the dominant type including over 80% of MAP isolates. VNTR typing of 527 MAP isolates identified 12 types, including “bison type” isolates, from seven different herds. At a national level, MAP isolates differed from each other by 1–2 to 239–240 SNPs, regardless of whether they belonged to the same or different VNTR types. A herd-level analysis of MAP isolates demonstrated that VNTR typing may both over-estimate and under-estimate the relatedness of MAP isolates found within a single herd.&lt;p&gt;&lt;/p&gt; Conclusions: The presence of multiple MAP subtypes in Canada suggests multiple introductions into the country including what has now become one dominant type, an important finding for Johne’s disease control. VNTR typing often failed to identify closely and distantly related isolates, limiting the applicability of using this typing scheme to study the molecular epidemiology of MAP at a national and herd-level.&lt;p&gt;&lt;/p&gt

Influence of citric acid and water on thermoplastic wheat flour/poly(lactic acid) blends. I: Thermal, mechanical and morphological properties

Wheat flour was plasticized with glycerol and compounded with poly(lactic acid) in a one-step twin-screw extrusion process in the presence of citric acid with or without extra water. The influence of these additives on process parameters and thermal, mechanical and morphological properties of injected samples from the prepared blends, was then studied. Citric acid acted as a compatibilizer by promoting depolymerization of both starch and PLA. For an extrusion without extra water, the amount of citric acid (2 parts for 75 parts of flour, 25 parts of PLA and 15 parts of glycerol) has to be limited to avoid mechanical properties degradation. Water, added during the extrusion, improved the whole process, minimizing PLA depolymerization, favoring starch plasticization by citric acid and thus improving phases repartition