Low-temperature protonation studies of transition metal alkyl complexes and the synthesis and characterization of early transition metal PCP pincer complexes and two-coordinate alkylamido complexes

We recently reported NMR studies of an osmium alkane complex, [Cp*Os(DFMPM)(CH4)]+, where Cp* is pentamethylcyclopentadienyl and DFMPM is bis(bis(trifluoromethyl)phosphino)methane. As part of an effort to continue these studies, the procedures to synthesize the DFMPM ligand and the Cp*Os(DFMPM)Br intermediate have been improved. A laboratory-scale procedure was developed to synthesize diethylzinc in which the α-CH2 positions are isotopically labeled with carbon-13 and/or deuterium; these reagents were then employed to synthesize isotopically labeled analogs of Cp*Os(DFMPM)Et. Protonation of Cp*Os(DFMPM)Et with HOTf in CDCl2F at -130 °C affords the alkane complex [Cp*Os(DFMPM)(CH3CH3)][OTf]. The dissociation of the ethane ligand follows first-order kinetics characterized by activation parameters of ΔH‡ = 14.4 ± 4.2 kcal/mol and ΔS‡ = 7 ± 20 cal mol-1 K-1. These values are within error for those of the methane analog, ΔH‡ = 14.9 ± 1.5 kcal/mol and ΔS‡ = 12.3 ± 8.8 cal mol-1 K-1. IPR studies of the ethane complex indicate that the ethane coordinates to [Cp*Os(DFMPM)]+ through a single hydrogen atom in either an η2- or κ1-fashion, depending on whether or not the carbon atom is significantly involved in the bonding interaction. The IPR studies afford chemical shifts of δT = 1.99 ± 0.17 and δB = -10.99 ± 0.32 for the terminal and bridging hydrogen atoms of the α-methyl group of the ethane ligand, respectively. δT for the ethane complex is significantly deshielded compared to the methane analog (δT = 0.39 ± 0.05) and δB for the ethane complex is significantly shielded compared to the methane analog (δB = -8.92 ± 0.17). These data support the hypothesis that the chemical shifts of the alkane ligand are significantly affected by diamagnetic anisotropy. The upfield chemical shift of the α-carbon in the 13C NMR spectra of the ethane and methane complexes can be explained in the same way, and are not necessarily indicative of a bonding interaction with osmium. Improvements were made to the procedures for the synthesis of (RPCP)M(CH3), where RPCP is a 2,6-bis(dialkylphosphinomethyl)phenyl pincer ligand and M is a group 10 transition metal. Complexes where R is isopropyl were prepared with nickel, palladium, and platinum. Additionally, complexes where R is t-butyl or adamantyl were prepared for nickel. Protonation of these complexes with HOTf in CDCl2F did not afford observable alkane complexes. In the cases of nickel and palladium, free alkane was generated even at -130 °C; the bonding interaction between the metal and the alkane is evidently very weak. In the case of platinum, protonation was slow until the reaction was warmed to -60 °C, at which point free alkane was generated; no alkyl/hydride or alkane coordination complexes could be observed. More electron-rich metal centers may be required to prepare alkane complexes of group 10 transition metals that can be studied by NMR spectroscopy. Procedures for the synthesis of(tBuPCP)TiCl2 and (tBuPCP)CrCl2(THF), where (tBuPCP) is 2,6-bis(di-tert-butylphosphinomethyl)phenyl, were developed. The titanium compound reacts with LiBH4 to afford (tBuPCP)Ti(BH4)2. (tBuPCP)CrCl2(THF) can be desolvated to afford (tBuPCP)CrCl2 by application of heat under vacuum. (tBuPCP)CrCl2 undergoes reduction and decomposition when treated with LiBH4 but affords the chromium(II) product (tBuPCP)CrCl when reduced by KC8. All compounds were characterized crystallographically. A multi-gram-scale synthetic procedure was developed for Mn(TMP)2, where TMP is 2,2,6,6-tetramethylpiperidide). Mn(TMP)2 is a potential precursor compound for the chemical vapor deposition of manganese nitride films. The compound was crystallographically characterized. The solid state structure of Mn(TMP)2 is isomorphous to that of its iron analog Fe(TMP)2

Fixed-bed column recirculation system for investigation of sorption and biodegradation of organic pollutants in saturated sediment: a detailed design and development

Background: Sorption and biodegradation are the primary processes of organic pollution remediation in aquatic and soil/sediment environments. While researchers have substantially reported their findings regarding these processes, little attention has been given to description of experimental apparatus. This technical paper aims to present the development and detailed design of a fixed-bed column recirculation (FBCR) system which has been widely applied to investigate sorption and biodegradation of organic pollutants in aquatic and/or sediment environments. Findings: The FBCR system was developed and tested by three experiments investigating sorption and biodegradation of two herbicides (isoproturon and mecoprop) in different saturated materials (hydrofilt and river sediment). Efficiency of the FBCR system was assessed according to criteria i.e. reliability, leaking inhibition, reproducibility, practical of use and cost. The results indicated that the latest version (Version 4) of the FBCR system has been significantly improved and ready to extend to similar studies. Conclusions: This system is therefore recommended to researchers who intend to investigate the remediation of organic pollutants in aquatic, soil and sediment environments

Low-Volume and High-Volume Readers of Neurological and Musculoskeletal MRI: Achieving Subspecialization in Radiology.

ObjectiveDifferentiate high- versus low-volume radiologists who interpret neurological (Neuro) MRI or musculoskeletal (MSK) MRI and measure the proportion of Neuro and MSK MRIs read by low-volume radiologists.MethodsWe queried the 2015 Medicare Physician and Other Supplier Public Use File for radiologists who submitted claims for Neuro or MSK MRIs. Radiologists were classified as high-volume versus low-volume based on their work relative value units (wRVUs) focus or volume of studies interpreted using three different methodologies: Method 1, percentage of wRVUs in Neuro or MSK MRI; Method 2, absolute number of Neuro or MSK MRIs interpreted; and Method 3, both percentage and absolute number. Multiple thresholds with each methodology were tested, and the percentage of Neuro or MSK MRIs interpreted by low-volume radiologists was calculated for each threshold.ResultsWith Method 1, 33% of Neuro MRI and 50% of MSK MRI studies were interpreted by a radiologist whose wRVUs in Neuro or MSK MRI were less than 20% (Method 1). With Method 2, 22% of Neuro MRIs and 37% of MSK MRIs were interpreted by radiologists who read fewer than the mean number of Neuro or MSK MRIs interpreted by an "average full-time radiologist" whose wRVUs in Neuro or MSK MRI were approximately 20%. With Method 3, 38% of Neuro MRIs and 57% of MSK MRIs were interpreted by "low-volume" radiologists. If instead a 50% wRVU threshold is used for Methods One, Two, and Three, then 70%, 58%, and 77% of Neuro MRIs and 86%, 80%, and 90% of MSK MRIs are read by low-volume radiologists.DiscussionA large number of radiologists read a low volume of Neuro or MSK MRIs; these low-volume Neuro or MSK MRI radiologists read a substantial portion of Neuro or MSK MRIs. It is unknown which of the methods for distinguishing low-volume radiologists, combined with which threshold, may best correlate with high-performing or low-performing radiologists

Aerial mucosalivary droplet dispersal distributions with implications for disease mitigation

We investigate mucosalivary dispersal and deposition on horizontal surfaces corresponding to human exhalations with physical experiments under still-air conditions. Synthetic fluorescence tagged sprays with size and speed distributions comparable to human sneezes are observed with high-speed imaging. We show that while some larger droplets follow parabolic trajectories, smaller droplets stay aloft for several seconds and settle slowly with speeds consistent with a buoyant cloud dynamics model. The net deposition distribution is observed to become correspondingly broader as the source height $H$ is increased, ranging from sitting at a table to standing upright. We find that the deposited mucosaliva decays exponentially in front of the source, after peaking at distance $x = 0.71$\,m when $H = 0.5$\,m, and $x = 0.56$\,m when $H=1.5$\,m, with standard deviations $\approx 0.5$\,m. Greater than 99\% of the mucosaliva is deposited within $x = 2$\,m, with faster landing times {\em further} from the source. We then demonstrate that a standard nose and mouth mask reduces the mucosaliva dispersed by a factor of at least a hundred compared to the peaks recorded when unmasked.Comment: See paper cite for S

Listening to the noise: random fluctuations reveal gene network parameters

The cellular environment is abuzz with noise originating from the inherent random motion of reacting molecules in the living cell. In this noisy environment, clonal cell populations show cell-to-cell variability that can manifest significant phenotypic differences. Noise-induced stochastic fluctuations in cellular constituents can be measured and their statistics quantified. We show that these random fluctuations carry within them valuable information about the underlying genetic network. Far from being a nuisance, the ever-present cellular noise acts as a rich source of excitation that, when processed through a gene network, carries its distinctive fingerprint that encodes a wealth of information about that network. We show that in some cases the analysis of these random fluctuations enables the full identification of network parameters, including those that may otherwise be difficult to measure. This establishes a potentially powerful approach for the identification of gene networks and offers a new window into the workings of these networks

HIV Suppression among Patients on Treatment in Vietnam: A Review of HIV Viral Load Testing in a Public Urban Clinic in Ho Chi Minh City

Background. There are few reports of HIV viral load (VL) testing among patients on ART in Vietnam. Methods. From a public clinic in Ho Chi Minh City (HCMC), we reviewed cases of VL measurements from adults on ART. Results. We identified 228 cases. Median age was 30 years (27–34), 85% were male, and 77% had a history of IDU. The mean ART duration was 26 months (95% CI 25–27); d4T/3TC/NVP was the most common regimen. Viral suppression was seen in 160/228 (70%). Viremia (>1000 copies/mL) was associated with prior ART exposure (OR 5.68, P < .0001) and immunologic failure (OR 4.69, P = .0001). Targeted testing accounted for 13% of cases, only half of which yielded viremia. Conclusion. We demonstrate a high HIV suppression rate among patients on ART in HCMC, Vietnam. In this setting, routine testing detects viremia missed by targeted testing

Reducing Geographic Disparities in Automatic Speech Recognition via Elastic Weight Consolidation

We present an approach to reduce the performance disparity between geographic regions without degrading performance on the overall user population for ASR. A popular approach is to fine-tune the model with data from regions where the ASR model has a higher word error rate (WER). However, when the ASR model is adapted to get better performance on these high-WER regions, its parameters wander from the previous optimal values, which can lead to worse performance in other regions. In our proposed method, we utilize the elastic weight consolidation (EWC) regularization loss to identify directions in parameters space along which the ASR weights can vary to improve for high-error regions, while still maintaining performance on the speaker population overall. Our results demonstrate that EWC can reduce the word error rate (WER) in the region with highest WER by 3.2% relative while reducing the overall WER by 1.3% relative. We also evaluate the role of language and acoustic models in ASR fairness and propose a clustering algorithm to identify WER disparities based on geographic region.Comment: Accepted for publication at Interspeech 202

An investigative study into the sensitivity of different partial discharge φ-q-n pattern resolution sizes on statistical neural network pattern classification

This paper investigates the sensitivity of statistical fingerprints to different phase resolution (PR) and amplitude bins (AB) sizes of partial discharge (PD) φ-q-n (phase-amplitude-number) patterns. In particular, this paper compares the capability of the ensemble neural network (ENN) and the single neural network (SNN) in recognizing and distinguishing different resolution sizes of φ-q-n discharge patterns. The training fingerprints for both the SNN and ENN comprise statistical fingerprints from different φ-q-n measurements. The result shows that there exists statistical distinction for different PR and AB sizes on some of the statistical fingerprints. Additionally, the ENN and SNN outputs change depending on training and testing with different PR and AB sizes. Furthermore, the ENN appears to be more sensitive in recognizing and discriminating the resolution changes when compared with the SNN. Finally, the results are assessed for practical implementation in the power industry and benefits to practitioners in the field are highlighted