The single-station microtremor horizontal-to-vertical spectral ratio (MHVSR) method was initially proposed to retrieve the site amplification function and its resonance frequencies produced by ...unconsolidated sediments overlying high-velocity bedrock. Presently, MHVSR measurements are predominantly conducted to obtain an estimate of the fundamental site frequency at sites where a strong subsurface impedance contrast exists. Of the earthquake site characterization methods presented in this special issue, the MHVSR method is the furthest behind in terms of consensus towards standardized guidelines and commercial use. The greatest challenges to an international standardization of MHVSR acquisition and analysis are (1) the
what
— the underlying composition of the microtremor wavefield is site-dependent, and thus, the appropriate theoretical (forward) model for inversion is still debated; and (2) the
how
— many factors and options are involved in the data acquisition, processing, and interpretation stages. This paper reviews briefly a historical development of the MHVSR technique and the physical basis of an MHVSR (the
what
). We then summarize recommendations for MHVSR acquisition and analysis (the
how
). Specific sections address MHVSR interpretation and uncertainty assessment.
Coordinatively unsaturated transition-metal compounds stabilized by supplemental electron donation from π-basic ligands are described as "operationally unsaturated". Such complexes are useful ...analogues of active catalyst structures that readily react with substrate molecules. We report that Ph
2
P(C
6
H
4
)NCHC(CH
3
)
2
−
(
L1
) effectively stabilizes Ru(
ii
) in an operationally unsaturated form. In the absence of Lewis bases, the 1-azaallyl group of
L1
dominantly coordinates through a κ
1
-N mode, but can readily and reversibly isomerize to an η
3
-NCC coordination mode to stabilize the metal. As an operationally unsaturated complex, Ru(Cp*)(
L1
) dimerizes at low temperature. At ambient temperature it rapidly reacts with pyridine or PPh
3
to form an adduct. These findings with
L1
demonstrate that changes in the hapticity of a 1-azaallyl fragment offer an alternative means to stabilize low-coordinate metals.
An operationally unsaturated ruthenium complex is stabilized by a ligand that can readily switch between different coordination modes.
Incorporation of a polar filler such as silica into a nonpolar rubber matrix is challenging and energy consuming due to their large difference in polarity. Epoxidation of carbon–carbon double bonds ...in unsaturated rubber, especially for rubber with low unsaturation such as butyl rubber, is an effective method to introduce polar functional groups to the rubber macromolecules for better filler dispersion. Although different epoxidation reagents including hydrogen peroxide (H2O2), peracid, and meta-chloroperoxybenzoic acid (mCPBA) have been previously reported, these reagents have different drawbacks. In this article, a metal-free epoxidation reagent, dimethyl dioxirane (DMDO), generated from acetone and Oxone is explored for efficient epoxidation of rubber with low unsaturation. The effects of the addition manner of the reactant Oxone and buffer sodium bicarbonate (NaHCO3) and reaction temperature on the epoxide formation are studied. Compared to peracid, a faster and more efficient epoxidation without the generation of a ring-opened product is achieved when DMDO is used as the epoxidation reagent. Furthermore, it is found that the epoxidation using DMDO is not sensitive to the water concentration in the rubber solution up to 20 wt %. The addition of quaternary ammonium salt as a phase transfer catalyst not only improves the conversion but also further increases the water tolerance to 25 wt %. The reaction conditions for preparation of epoxidized butyl rubber with different percentages of epoxide group are optimized by Design of Experiments (DoE). At the end, improved dispersion of silica in the matrix of epoxidized butyl rubber is achieved, as revealed by the rubber process analyzer (RPA) and atomic force microscopy (AFM).
Crustal magnetic anomaly maps over oceanic regions are based largely on marine trackline surveys. These surveys, collected from the 1950s to the present, span a wide range of data quality and ...reliability. We discuss a methodology for constructing grids from these data with associated cell by cell estimates of grid uncertainty. The method is tested with a modern airborne survey for a representative region in the eastern Caribbean. The results are promising, producing an uncertainty estimate that is accurate to one standard deviation for the test area. As magnetic anomaly maps and grids are increasingly applied as constraints for geologic interpretation as well as for alternative navigation (e.g., navigation by magnetic field patterns in the absence of GPS), it is important to quantify the accuracy of these maps.
Plain Language Summary
It is challenging to make maps of the variations in the Earth's magnetic field, called crustal magnetic anomalies, caused by the distribution of magnetic minerals in oceanic areas. The reason for this is that the best available data for most marine areas is from ship‐based measurements collected over many decades, from the 1950s to the present. The spatial distribution of these marine survey tracklines is highly variable as is their original data quality and reliability. Previous grids and maps constructed from marine trackline data have not included systematic estimation of the grid/map uncertainty. At best, earlier maps have included generalized statements about the estimated mean uncertainty. In this study, we present a methodology for estimating the crustal magnetic anomaly and the associated uncertainty from marine trackline data. The method is evaluated using a modern airborne survey of a test area in the eastern Caribbean, an area surrounding St. Croix in the US Virgin Islands.
Key Points
Marine crustal magnetic anomaly maps are typically constructed from trackline data with variable uncertainties and spatial configurations
This paper presents a methodology for creating data grids with associated cell by cell uncertainty from marine trackline data
The method is tested against newly collected modern airborne magnetic data
This paper describes two methods of eye detection in a face image. The face is first detected as a large flesh-colored region, and anthropometric data are then used to estimate the size and ...separation of the eyes. When a linear filtering method, using filters based on Gabor wavelets, was then applied to detect the eyes in the gray-level image of the face, the detection rate was good (80% on one dataset, 95% on another), but there were many false alarms. A nonlinear filtering method was therefore developed to detect the corners of the eyes in the color image of the face. This method gave a 90% detection rate with no false alarms.
Dye‐dye conjugates have attracted significant interest for their utility in applications such as bioimaging, theranostics, and light‐harvesting. Many classes of organic dyes have been employed in ...this regard; however, building blocks don't typically extend beyond small chromophores. This can lead to minor changes to the optoelectronic properties of the original dye. The exploration of dye–dye structures is impeded by long synthetic routes, incompatible synthetic conditions, or a mismatch of the desired properties. Here, we present the first‐of‐their‐kind dye‐dye conjugates of boron difluoride complexes of formazanate and dipyrromethene ligands. These conjugates exhibit dual photoluminescence bands that reach the near‐infrared spectral region and implicate anti‐Kasha processes. Cyclic voltammetry experiments revealed the generation of polyanionic species that can reversibly tolerate the uptake of up to 6 electrons. Ultimately, we demonstrate that BF2 formazanates can serve as a synthetically accessible platform to build upon new classes of dye‐dye conjugates.
The first examples of BF2 formazanate and BODIPY conjugates: Dyads and triads of BF2 formazanate and BODIPY dyes undergo reversible reduction to polyanions and exhibit anti‐Kasha photoluminescence. These properties arise from the interplay of the discrete properties of each dye and highlight the promise of dye‐dye conjugates based on BF2 formazanates.
The mechanism of zirconium-catalyzed hydroaminoalkylation of diphenylacetylene, and the origin of the contrasting reactivity with N-benzylaniline or N-(trimethylsilyl)benzylamine substrates, have ...been investigated. Isolated intermediates have revealed that the nature of the C–H activation and C–C bond-forming steps in alkyne hydroaminoalkylation are analogous to those of the alkene variant, regardless of the amine substrate. In the zirconium-catalyzed hydroaminoalkylation of alkynes, the open coordination sphere at the zirconium center, supported by the bis(ureate) ligand, enables the coordination of neutral protic donors. This is essential for promoting catalytic turnover in these reactions. Under catalytic conditions, dimethylamine acts as a proton source for releasing the allylic amine products while minimizing the formation of side products. Additionally, we identified the formation of a homoleptic tetra(ureate) zirconium complex as the main catalyst decomposition pathway in catalytic alkyne hydroaminoalkylation. The formation of similar homoleptic structures is further favored when employing smaller bis(urea) proligands, thus explaining the poor performance of some ligands in catalysis. However, further increasing the bis(urea) proligand size to minimize such catalyst decomposition favors isomerization side-products resulting in reduced yields of the desired product. This study provides ligand design principles that guide the development of coordinatively flexible catalysts to achieve catalytic turnover in systems that rely upon protonolysis steps, as in hydroaminoalkylation.
Thin-slice computer tomography provides high-resolution images that facilitate the diagnosis of early-stage lung cancer. However, the sheer size of the CT volumes introduces variability in ...radiological readings, driving the need for automated detection systems. The main contribution of this paper is a technique for combining geometric and intensity models with the analysis of local curvature for detecting pulmonary lesions in CT. The local shape at each voxel is represented via the principal curvatures of its associated isosurface without explicitly extracting the isosurface. The comparison of these curvatures to values derived from analytical shape models is then used to label the voxel as belonging to particular anatomical structures, e.g., nodules or vessels. The algorithm was evaluated on 242 CT exams with expert-determined ground truth. The performance of the algorithm is quantified by free-response receiver-operator characteristic curves, as well as by its potential for improvement in radiologist sensitivity.
Seismic site effects arise from local geologic and topographic conditions, and modify incident earthquake ground motions at a site. Understanding variability in seismic site conditions is necessary ...for accurate assessment of seismic hazard. The microtremor horizontal to vertical spectral ratio (mHVSR) method is a cost-effective and non-invasive method to measure the site’s filtering effect in terms of an amplification frequency spectrum. Using a large, compiled database of mHVSR measurements from the Metropolitan Vancouver area, the impact of acquisition and processing parameter choices on the computed mHVSR is investigated. A robust processing algorithm is developed to batch process high-quantity mHVSR datasets. Products related to seismic microzonation hazard mapping, such as a regional map of the site fundamental frequency and the suite of unique mHVSR amplification spectra in the region are provided. This thesis exemplifies the practicality of using the mHVSR method for seismic site characterization.
This paper presents a model-based technique for lesion detection in colon CT scans that uses analytical shape models to map the local shape curvature at individual voxels to anatomical labels. Local ...intensity profiles and curvature information have been previously used for discriminating between simple geometric shapes such as spherical and cylindrical structures. This paper introduces novel analytical shape models for colon-specific anatomy, viz. folds and polyps, built by combining parts with simpler geometric shapes. The models better approximate the actual shapes of relevant anatomical structures while allowing the application of model-based analysis on the simpler model parts. All parameters are derived from the analytical models, resulting in a simple voxel labeling scheme for classifying individual voxels in a CT volume. The algorithm’s performance is evaluated against expert-determined ground truth on a database of 42 scans and performance is quantified by free-response receiver-operator curves.
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