Full-waveform inversion FWI is a challenging data-fitting procedure based on full-wavefield modeling to extract quantitative information from seismograms. High-resolution imaging at half the propagated wavelength is expected. Recent advances in high-performance computing and multifold/multicomponent wide-aperture and wide-azimuth acquisitions make 3D acoustic FWI feasible today. Key ingredients of FWI are an efficient forward-modeling engine and a local differential approach, in which the gradient and the Hessian operators are efficiently estimated. Local optimization does not, however, prevent convergence of the misfit function toward local minima because of the limited accuracy of the starting model, the lack of low frequencies, the presence of noise, and the approximate modeling of the wave-physics complexity. Different hierarchical multiscale strategiesaredesignedtomitigatethenonlinearityandill-posedness of FWI by incorporating progressively shorter wavelengths in the parameter space. Synthetic and real-data case studies address reconstructing various parameters, from VP and VS velocities to density, anisotropy, and attenuation. This review attempts to illuminate the state of the art of FWI. Crucial jumps, however, remain necessary to make it as popular as migration techniques. The challenges can be categorized as 1 building accurate starting models with automatic procedures and/or recording low frequencies, 2 defining new minimization criteria to mitigate the sensitivity of FWI to amplitude errors and increasing the robustness of FWI when multiple parameter classes are estimated, and 3 improving computational efficiency by data-compression techniquestomake3DelasticFWIfeasible.

/pdf/an-overview-of-full-waveform-inversion-in-exploration-59sei7fzvh.pdf

An overview of full-waveform inversion in exploration geophysics

The brain and nervous system are prone to oxidative stress, and are inadequately equipped with antioxidant defense systems to prevent 'ongoing' oxidative damage, let alone the extra oxidative damage imposed by the neurodegenerative diseases. Indeed, increased oxidative damage, mitochondrial dysfunction, accumulation of oxidized aggregated proteins, inflammation, and defects in protein clearance constitute complex intertwined pathologies that conspire to kill neurons. After a long lag period, therapeutic and other interventions based on a knowledge of redox biology are on the horizon for at least some of the neurodegenerative diseases.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1471-4159.2006.03907.x

Oxidative stress and neurodegeneration: where are we now?

Advances in metal-induced oxidative stress and human disease

We are just beginning to understand the metabolism of heavy metals and to use their metabolic functions in biotechnology, although heavy metals comprise the major part of the elements in the periodic table. Because they can form complex compounds, some heavy metal ions are essential trace elements, but, essential or not, most heavy metals are toxic at higher concentrations. This review describes the workings of known metal-resistance systems in microorganisms. After an account of the basic principles of homoeostasis for all heavy-metal ions, the transport of the 17 most important (heavy metal) elements is compared.

Microbial heavy-metal resistance

Natural products: a continuing source of novel drug leads.

Numerical simulations are used to compare the resolution and efficiency of 2D resistivity imaging surveys for 10 electrode arrays. The arrays analysed include polepole (PP), pole-dipole (PD), half-Wenner (HW), Wenner-α (WN), Schlumberger (SC), dipole-dipole (DD), Wenner-β (WB), γ -array (GM), multiple or moving gradient array (GD) and midpoint-potential-referred measurement (MPR) arrays. Five synthetic geological models, simulating a buried channel, a narrow conductive dike, a narrow resistive dike, dipping blocks and covered waste ponds, were used to examine the surveying efficiency (anomaly effects, signal-to-noise ratios) and the imaging capabilities of these arrays. The responses to variations in the data density and noise sensitivities of these electrode configurations were also investigated using robust (L1-norm) inversion and smoothness-constrained least-squares (L2-norm) inversion for the five synthetic models. The results show the following. (i) GM and WN are less contaminated by noise than the other electrode arrays. (ii) The relative anomaly effects for the different arrays vary with the geological models. However, the relatively high anomaly effects of PP, GM and WB surveys do not always give a high-resolution image. PD, DD and GD can yield better resolution images than GM, PP, WN and WB, although they are more susceptible to noise contamination. SC is also a strong candidate but is expected to give more edge effects. (iii) The imaging quality of these arrays is relatively robust with respect to reductions in the data density of a multi-electrode layout within the tested ranges. (iv) The robust inversion generally gives better imaging results than the L2-norm inversion, especially with noisy data, except for the dipping block structure presented here. (v) GD and MPR are well suited to multichannel surveying and GD may produce images that are comparable to those obtained with DD and PD. Accordingly, the GD, PD, DD and SC arrays are strongly recommended for 2D resistivity imaging, where the final choice will be determined by the expected geology, the purpose of the survey and logistical considerations.

/pdf/a-numerical-comparison-of-2d-resistivity-imaging-with-10-1kfer57nmn.pdf

A numerical comparison of 2D resistivity imaging with 10 electrode arrays

Hallervorden-Spatz syndrome (HSS) is an autosomal recessive neurodegenerative disorder associated with iron accumulation in the brain. Clinical features include extrapyramidal dysfunction, onset in childhood, and a relentlessly progressive course. Histologic study reveals iron deposits in the basal ganglia. In this respect, HSS may serve as a model for complex neurodegenerative diseases, such as Parkinson disease, Alzheimer disease, Huntington disease and human immunodeficiency virus (HIV) encephalopathy, in which pathologic accumulation of iron in the brain is also observed. Thus, understanding the biochemical defect in HSS may provide key insights into the regulation of iron metabolism and its perturbation in this and other neurodegenerative diseases. Here we show that HSS is caused by a defect in a novel pantothenate kinase gene and propose a mechanism for oxidative stress in the pathophysiology of the disease.

A novel pantothenate kinase gene ( PANK2 ) is defective in Hallervorden-Spatz syndrome

Background Hallervorden–Spatz syndrome is an autosomal recessive disorder characterized by dystonia, parkinsonism, and iron accumulation in the brain. Many patients with this disease have mutations in the gene encoding pantothenate kinase 2 (PANK2); these patients are said to have pantothenate kinase–associated neurodegeneration. In this study, we compared the clinical and radiographic features of patients with Hallervorden–Spatz syndrome with and without mutations in PANK2. Methods One hundred twenty-three patients from 98 families with a diagnosis of Hallervorden–Spatz syndrome were classified on the basis of clinical assessment as having classic disease (characterized by early onset with rapid progression) or atypical disease (later onset with slow progression). Their genomic DNA was sequenced for PANK2 mutations. Results All patients with classic Hallervorden–Spatz syndrome and one third of those with atypical disease had PANK2 mutations. Whereas almost all mutations in patients with atypical disease ...

https://www.nejm.org/doi/pdf/10.1056/NEJMoa020817

Genetic, clinical, and radiographic delineation of Hallervorden-Spatz syndrome.

The molecular mechanisms responsible for the cellular uptake of copper in mammalian cells are unknown. We describe isolation of a human gene involved in this process by complementation of the yeast high-affinity copper uptake mutant, ctr1. Besides complementing ctr1 growth defect on nonfermentable media, the human gene also rescues iron transport and SOD1 defects in ctr1 yeast. Overexpression of the gene in yeast leads to vulnerability to the toxicity of copper overload. In addition, its expression in ctr1 yeast significantly increases the level of cellular copper, as demonstrated by atomic absorption. We propose this gene as a candidate for high-affinity copper uptake in humans and by analogy have named it hCTR1. The hCTR1 and yeast CTR1 predicted transmembrane proteins are 29% identical, but the human protein is substantially smaller in both the extracellular metal-binding and intracellular domains. An additional human gene similar to hCTR1, here named hCTR2, was identified in a database search. Both hCTR1 and hCTR2 are expressed in all human tissues examined, and both genes are located in 9q31/32. These studies, together with the previously recognized functional and sequence similarity between the Menkes/Wilson copper export proteins and CCC2 in yeast, demonstrate that similar copper homeostatic mechanisms are used in these evolutionarily divergent organisms.

https://www.pnas.org/content/pnas/94/14/7481.full.pdf

hCTR1: A human gene for copper uptake identified by complementation in yeast

The rare inherited condition acrodermatitis enteropathica (AE) results from a defect in the absorption of dietary zinc. Recently, we used homozygosity mapping in consanguineous Middle Eastern kindreds to localize the AE gene to an ∼3.5-cM region on 8q24. In this article, we identify a gene, SLC39A4, located in the candidate region and, in patients with AE, document mutations that likely lead to the disease. The gene encodes a histidine-rich protein, which we refer to as “hZIP4,” which is a member of a large family of transmembrane proteins, some of which are known to serve as zinc-uptake proteins. We show that Slc39A4 is abundantly expressed in mouse enterocytes and that the protein resides in the apical membrane of these cells. These findings suggest that the hZIP4 transporter is responsible for intestinal absorption of zinc.

Bing Zhou

Papers

A numerical comparison of 2D resistivity imaging with 10 electrode arrays

A novel pantothenate kinase gene ( PANK2 ) is defective in Hallervorden-Spatz syndrome

Genetic, clinical, and radiographic delineation of Hallervorden-Spatz syndrome.

hCTR1: A human gene for copper uptake identified by complementation in yeast

A Novel Member of a Zinc Transporter Family Is Defective in Acrodermatitis Enteropathica