In addition to the nucleophile and solvent, the leaving group has a significant influence on SN2 nucleophilic substitution reactions. Its role is frequently discussed with respect to reactivity, but ...its influence on the reaction dynamics remains unclear. Here, we uncover the influence of the leaving group on the gas-phase dynamics of SN2 reactions in a combined approach of crossed-beam imaging and dynamics simulations. We have studied the reaction F(-) + CH3Cl and compared it to F(-) + CH3I. For the two leaving groups, Cl and I, we find very similar structures and energetics, but the dynamics show qualitatively different features. Simple scaling of the leaving group mass does not explain these differences. Instead, the relevant impact parameters for the reaction mechanisms are found to be crucial and the differences are attributed to the relative orientation of the approaching reactants. This effect occurs on short timescales and may also prevail in solution-phase conditions.
Abstract Due to the necessary transition to renewable energy, the transport of electricity over long distances will become increasingly important, since the sites of sustainable electricity ...generation, such as wind or solar power parks, and the place of consumption can be very far apart. Currently, electricity is mainly transported via overhead AC lines. However, studies have shown that for long distances, transport via DC offers decisive advantages. To make optimal use of the existing route infrastructure, simultaneous AC and DC, or hybrid transmission, should be employed. The resulting electric field strengths must not exceed legally prescribed thresholds to avoid potentially harmful effects on humans and the environment. However, accurate quantification of the resulting electric fields is a major challenge in this context, as they can be easily distorted (e.g. by the measurement equipment itself). Nonetheless knowledge of the undisturbed field strengths from DC up to several multiples of the fundamental frequency of the power-grid (up to 1 kHz) is required to ensure compliance with the thresholds. Both AC and DC electric fields can result in the generation of corona ions in the vicinity of the line. In the case of pure AC fields, the corona ions generated typically recombine in the immediate vicinity of the line and, therefore, have no influence on the field measurement further away. Unfortunately, this assumption does not hold for DC fields and hybrid fields, where corona ions can be transported far away from the line (e.g. by wind), and potentially interact with the measurement equipment yielding incorrect measurement results. This review will provide a comprehensive overview of the current state-of-the-art technologies and methods which have been developed to address the problems of measuring the electric field near hybrid power lines.
Abstract
Spectral fingerprints of molecules are mostly accessible in the terahertz (THz) and mid-infrared ranges, such that efficient molecular-detection technologies rely on broadband coherent light ...sources at such frequencies. If THz Quantum Cascade Lasers can achieve octave-spanning bandwidth, their tunability and wavelength selectivity are often constrained by the geometry of their cavity. Here we introduce an adaptive control scheme for the generation of THz light in Quantum Cascade Random Lasers, whose emission spectra are reshaped by applying an optical field that restructures the permittivity of the active medium. Using a spatial light modulator combined with an optimization procedure, a beam in the near infrared (NIR) is spatially patterned to transform an initially multi-mode THz random laser into a tunable single-mode source. Moreover, we show that local NIR illumination can be used to spatially sense complex near-field interactions amongst modes. Our approach provides access to new degrees of freedom that can be harnessed to create broadly-tunable sources with interesting potential for applications like self-referenced spectroscopy.
The proton transfer reaction H3 + + CO is one of the cornerstone chemical processes in the interstellar medium. Here, the dynamics of this reaction have been investigated using crossed beam velocity ...map imaging. Formyl product cations are found to be predominantly scattered into the forward direction irrespective of the collision energy. In this process, a high amount of energy is transferred to internal product excitation. By fitting a sum of two distribution functions to the measured internal energy distributions, the product isomer ratio is extracted. A small HOC+ fraction is obtained at a collision energy of 1.8 eV, characterized by an upper limit of 24% with a confidence level of 84%. At lower collision energies, the data indicate purely HCO+ formation. Such low values are unexpected given the previously predicted efficient formation of both HCO+ and HOC+ isomers for thermal conditions. This is discussed in light of the direct reaction dynamics that are observed.
Background
Dysphagia and non‐cardiac chest pain are common symptoms associated with a novel hypercontractile disorder, namely Jackhammer esophagus (JE). The aim of this study was to explore these ...symptoms in patients with JE and to elucidate associations with disease defining metrics, crucial for subsequent therapies.
Methods
All consecutive patients, who were referred between January 2014 and December 2016 and fulfilled the criteria for JE were included in this study. Exclusion criteria were opioid intake, previous gastrointestinal surgery, mechanical esophageal obstruction and diseases explaining their symptoms.
Key Results
Of 2205 examined subjects, thirty patients (females: n = 17, 56.7%) with a median age of 58 (51.6‐64.9) years were finally enrolled. Dysphagia was noted in 53.3% (n = 16), whereas non‐cardiac chest pain was specified within 40% (n = 12) with symptom duration of up to 10 years. Perception of dysphagia (P = .03) and presence of both symptoms (P = .008) increased to the end of the study period. Dysphagia was significantly associated with distal contractile integral (DCI) scores of all (P = .023), hypercontractile (P = .011) and maximum DCI swallows (P = .008). Symptoms duration influenced hypercontractile DCI scores (P = .015, r = .438) and significantly correlated with the intensity of perceived dysphagia (P = .01, r = .585). Presence of non‐cardiac chest pain was not associated with any of these metrics.
Conclusions & Interferences
The DCI mediates dysphagia in patients with JE. Duration of symptoms affected hypercontractile DCI scores and aggravated perception of dysphagia indicating a progressive character of disease.
The distal contractile integral mediates dysphagia in patients with Jackhammer esophagus. Duration of symptoms had an impact on prevalence of dysphagia and severity indicating a progressive character of disease.
Fc‐dependent effector mechanisms may contribute to antibody‐mediated rejection (ABMR), and distinct gene polymorphisms modifying the function of Fc gamma receptors (FcγRs) may influence the ...capability of donor‐specific antibodies (DSAs) to trigger inflammation. To evaluate the relevance of functional FcγR variants in late ABMR, 85 DSA‐positive kidney allograft recipients, who were recruited upon antibody screening of 741 prevalent patients, were genotyped for polymorphisms in FcγRIIA (FCGR2A‐H/R131; rs1801274), FcγRIIIA (FCGR3A‐V/F158; rs396991), and FcγRIIIB (FCGR3B‐neutrophil antigen 1 (NA1/NA2; rs35139848). Individuals with high‐affinity FCGR3A‐V158 alleles (V/V158 or V/F158) showed a higher rate (and extent) of peritubular capillaritis (ptc) in protocol biopsies than homozygous carriers of the lower‐affinity allele (ptc score ≥1: 53.6% vs 25.9%; P = .018). Associations were independent of C1q‐binding to DSA or capillary C4d. In parallel, there was a trend toward increased macrophage‐ and injury‐repair response–associated transcript subsets. Kidney function over 24 months, however, was not different. In support of a functional role of FcγRIIIA polymorphism, NK92 cells expressing FCGR3A‐V158 produced >2 times as much interferon gamma upon incubation with HLA antibody‐coated cells as those expressing FCGR3A‐F158. FcγRIIA and FcγRIIIB polymorphisms were not associated with allograft morphology. Our data suggest that the presence of high‐affinity FcγRIIIA variants may favor DSA‐triggered microcirculation inflammation.
This cross‐sectional study performed in kidney transplant recipients with donor‐specific antibodies suggests that the presence of high‐functional variants of Fc gamma receptor IIIA favors antibody‐triggered microcirculation inflammation independent of complement activation, supporting an important role of Fc receptor‐dependent mechanisms of injury.
•We present a way to utilize the air damping as a design feature for laterally oscillating MEMS/MOEMS.•We show that it is possible to adjust the passive damping in a wide range.•MOEMS vibration ...sensors with different quality factors are presented confirming the results of the underlying analytical and numerical models.
The damping of an oscillator is, next to the effective mass and the stiffness, one of the key parameters that determine its frequency response as well as its noise. Since there are numerous different applications for oscillating microstructures, there are also numerous requirements for the shape of the respective resonance peak. While fabricating the right mass and stiffness to obtain a desired resonance frequency is, in general, a basic task, designing a micro-oscillator featuring an intended damping is not trivial. We present a way of utilizing the surrounding air to adjust the passive damping of a laterally oscillating micromechanical system. This is shown to hold in a relatively wide range by comparing analytical models and finite volume method simulations with measurements of a number of micro-electro-mechanical test structures with optical readout.
Background
Obesity and gastroesophageal reflux disease (GERD) are major health problems showing an inconstant relationship in the literature. Therefore, anthropometric parameters which are predictive ...and can simply be assessed at first patient presentation may lead to a better patient selection for ambulatory reflux monitoring. We aimed to examine the association of body mass index (BMI) and waist to hip ratio (WHR) with gastroesophageal reflux activity during 24 hour‐pH‐impedance monitoring.
Methods
Seven hundred and seventy‐one patients with GERD symptoms underwent 24 hour‐pH‐impedance monitoring and high resolution manometry off proton pump inhibitors. Patients with known primary motility disorders of the esophagus and pre‐existing endoscopic or operative procedure on esophagus or stomach were excluded from the study. Reflux parameters and anthropometric and demographic data from our prospectively gathered database were analyzed. We performed univariate and multivariate regression analysis to evaluate the associations of BMI and WHR with reflux parameters measured with 24 hour‐pH‐impedance monitoring.
Key Results
WHR showed a significantly stronger association with esophageal acid exposure than BMI (P<.001). Our data show that 6.9% of the percentage of endoluminal pH<4 in the distal esophagus is attributable to WHR. Furthermore, an association of WHR with impaired esophageal acid clearance was observed. Additionally, we observed an inverse relationship between lower esophageal sphincter integrity (P=.05) and esophageal acid exposure.
Conclusions and Inferences
WHR is a better predictor for esophageal acid exposure than BMI. Biomechanical and metabolic mechanisms of central fat distribution may influence reflux parameters in 24 hour pH impedance monitoring, which may affect patient selection for ambulatory reflux monitoring.
WHR is associated with the mean clearance time of acid from the distal esophagus (lct, logarithm of mean acid clearance time; hwr, waist to hip ratio)
•We present an analytical model for the air damping of laterally oscillating MEMS/MOEMS.•It agrees well with both measurement and numerical simulations.•We also show how holes in the laterally moving ...plate affect the quality facor of the device.
We report on an analytical model for the air damping of laterally oscillating MEMS and MOEMS following up on our recent paper 1. It can be used to more efficiently design micromechanical devices with tailor-made Q-factors for specific applications. The surface force responsible for the air damping was divided into contributions which were investigated separately. These include squeeze-film damping and the viscous forces responsible for shear wave emission and Couette type flow. Since the squeezing part is mostly underestimated in the current models, we applied more appropriate boundary conditions during the solution of Reynold's lubrication equation. The viscous contributions were investigated with respect to how holes – due to fabrication process or readout – in the moving plate affect the damping. We tested this model against FVM computations (OpenFOAM) and measurements of MOEMS test devices. It was in good agreement with both.
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