scholarly journals Linking Mechanistic Analysis of Catalytic Reactivity Cliffs to Ligand Classification

2021 ◽  
Author(s):  
Samuel Newman-Stonebraker ◽  
Sleight Smith ◽  
Julia Borowski ◽  
Ellyn Peters ◽  
Tobias Gensch ◽  
...  
Keyword(s):  
Molecular Descriptors ◽  
Threshold Value ◽  
Phosphine Ligands ◽  
Quantitative Classification ◽  
Mechanistic Analysis ◽  
Mechanistic Investigation ◽  
Similar Threshold ◽  
Specific Structural Feature ◽  
Catalytic Reactivity ◽  
Data Driven Modeling

Statistical analysis of reaction data with molecular descriptors can enable chemists to identify reactivity cliffs that result from a mechanistic dependence on a specific structural feature. In this study, we develop a broadly applicable and quantitative classification workflow that identifies reactivity cliffs in eleven Ni- and Pd-catalyzed cross-coupling datasets employing monodentate phosphine ligands. A unique ligand steric descriptor, %<i>V</i><sub>bur</sub> (<i>min</i>), is found to divide these datasets into active and inactive regions at a similar threshold value. Organometallic studies demonstrate that this threshold corresponds to the binary outcome of bisligated versus monoligated metal and that %<i>V</i><sub>bur</sub> (<i>min</i>) is a physically meaningful and predictive representation of ligand structure in catalysis. Taken together, we expect that this strategy will be of broad value in mechanistic investigation of structure-reactivity relationships, while providing a means to rationally partition datasets for data-driven modeling.

scholarly journals Linking Mechanistic Analysis of Catalytic Reactivity Cliffs to Ligand Classification

2021 ◽  
Author(s):  
Samuel Newman-Stonebraker ◽  
Sleight Smith ◽  
Julia Borowski ◽  
Ellyn Peters ◽  
Tobias Gensch ◽  
...  
Keyword(s):  
Molecular Descriptors ◽  
Threshold Value ◽  
Phosphine Ligands ◽  
Quantitative Classification ◽  
Mechanistic Analysis ◽  
Mechanistic Investigation ◽  
Similar Threshold ◽  
Specific Structural Feature ◽  
Catalytic Reactivity ◽  
Data Driven Modeling

Statistical analysis of reaction data with molecular descriptors can enable chemists to identify reactivity cliffs that result from a mechanistic dependence on a specific structural feature. In this study, we develop a broadly applicable and quantitative classification workflow that identifies reactivity cliffs in eleven Ni- and Pd-catalyzed cross-coupling datasets employing monodentate phosphine ligands. A unique ligand steric descriptor, %<i>V</i><sub>bur</sub> (<i>min</i>), is found to divide these datasets into active and inactive regions at a similar threshold value. Organometallic studies demonstrate that this threshold corresponds to the binary outcome of bisligated versus monoligated metal and that %<i>V</i><sub>bur</sub> (<i>min</i>) is a physically meaningful and predictive representation of ligand structure in catalysis. Taken together, we expect that this strategy will be of broad value in mechanistic investigation of structure-reactivity relationships, while providing a means to rationally partition datasets for data-driven modeling.

Collisional Energy Deposition Threshold for Extended Damage Depths in Ion-Implanted Silicates

1991 ◽  
Vol 235 ◽  
Author(s):  
G. W. Arnold ◽  
G. Battaglin ◽  
A. Boscolo-Boscoletto ◽  
F. Caccavalle ◽  
G. De Marchi ◽  
...  
Keyword(s):  
Energy Deposition ◽  
Etching Rate ◽  
Threshold Value ◽  
Critical Energy ◽  
Fused Silica ◽  
Crystalline Quartz ◽  
Collisional Energy ◽  
Show Evidence ◽  
Similar Threshold ◽  
Induced Changes

ABSTRACTMany properties of implanted fused silica (e.g., surface stress, hardness) exhibit maximum implantation-induced changes for collisional energy deposition values of ∼1020 keV/cm3. We have observed a second critical energy deposition threshold value of about 1022 keV/cm3 in stress and hardness measurements as well as in many other experiments on silicate glasses (leaching, alkali depletion, etching rate, gaseous implant redistribution). The latter show evidence for damage depths exceeding TRIM ranges by about a factor of 2. For crystalline quartz, a similar threshold value value has been found for extended damage depths (greater than TRIM) for 250 kev ions (H-Au) as measured by RBS and interference fringes. This phenomenon at high damage deposition energy may involve the large stress gradients between damaged and undamaged regions and the much increased diffusion coefficient for defect transport.

scholarly journals Mechanistic investigation of benzene esterification by K2CO3/TiO2: the catalytic role of the multifunctional interface

2021 ◽  
Author(s):  
Jittima Meeprasert ◽  
Guanna Li ◽  
Evgeny A Pidko
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Efficient Catalyst ◽  
Functional Theory ◽  
Mechanistic Investigation ◽  
Tio2 Support ◽  
Catalytic Role ◽  
Catalytic Reactivity

Potassium carbonate dispersed over defective TiO2 support (K2CO3/TiO2) is an efficient catalyst for benzene esterification with CO2 and CH3OH. Density functional theory calculations reveal that this unique catalytic reactivity originates...

In situ irradiation effects studies in medium- and high-voltage TEM

1995 ◽  
Vol 53 ◽  
pp. 234-235
Author(s):  
Charles W. Allen
Keyword(s):  
Cross Section ◽  
Particle Flux ◽  
Threshold Value ◽  
High Energy ◽  
Irradiation Damage ◽  
Defect Complexes ◽  
Lattice Position ◽  
Electrons And Ions ◽  
The Masses

With respect to structural consequences within a material, energetic electrons, above a threshold value of energy characteristic of a particular material, produce vacancy-interstial pairs (Frenkel pairs) by displacement of individual atoms, as illustrated for several materials in Table 1. Ion projectiles produce cascades of Frenkel pairs. Such displacement cascades result from high energy primary knock-on atoms which produce many secondary defects. These defects rearrange to form a variety of defect complexes on the time scale of tens of picoseconds following the primary displacement. A convenient measure of the extent of irradiation damage, both for electrons and ions, is the number of displacements per atom (dpa). 1 dpa means, on average, each atom in the irradiated region of material has been displaced once from its original lattice position. Displacement rate (dpa/s) is proportional to particle flux (cm-2s-1), the proportionality factor being the “displacement cross-section” σD (cm2). The cross-section σD depends mainly on the masses of target and projectile and on the kinetic energy of the projectile particle.

Ein objektanalytisches Verfahren zur Bestimmung der Fläche des nuklidspeichemden Schilddrüsenparenchyms im Szintigramm

1991 ◽  
Vol 30 (01) ◽  
pp. 31-34
Author(s):  
R. Kodym ◽  
R. Seyss
Keyword(s):  
Threshold Value ◽  
Thyroid Uptake

An algorithm for object isolation was developed to determine the area of the thyroid in scintigraphic images, and its volume calculated therefrom so that operator-induced variations, common if the usual manual technique is used, could be avoided. The object isolation is performed for every possible threshold value. The resulting object isolation curves give a reliable and reproducible thyroid area. The method may be used routinely except in cases of blocked thyroid uptake or of multiple autonomous adenomas.

Aktivitätskonzentration der vom Personal einer Radiojodtherapiestation eingeatmeten Luft

1987 ◽  
Vol 26 (03) ◽  
pp. 143-146 ◽  
Author(s):  
H. Fill ◽  
M. Oberladstätter ◽  
J. W. Krzesniak
Keyword(s):  
Nuclear Medicine ◽  
Length Of Stay ◽  
Activity Concentration ◽  
Threshold Value ◽  
Whole Body ◽  
Therapeutic Activity ◽  
External Radiation ◽  
Oral Application ◽  
Exhaled Air ◽  
The Mean

The mean activity concentration of1311 during inhalation by the nuclear medicine personnel was measured at therapeutic activity applications of 22 GBq (600 mCi) per week. The activity concentration reached its maximum in the exhaled air of the patients 2.5 to 4 hours after oral application. The normalized maximum was between 2 • 10−5 and 2 • 10−3 Bq-m−3 per administered Bq. The mean activity concentration of1311 inhaled by the personnel was 28 to 1300 Bq-m−3 (0.8 to 35 nCi-rrf−3). From this the1311 uptake per year was estimated to be 30 to 400 kBq/a (x̄ = 250, SD = 50%). The maximum permitted uptake from air per year is, according to the German and Austrian radiation protection ordinances 22/21 µiCi/a (= 8 • 105 Bq/a). At maximum 50% and, on the average, 30% of this threshold value are reached. The length of stay of the personnel in the patient rooms is already now limited to such an extent that 10% of the maximum permissible whole-body dose for external radiation is not exceeded. Therefore, increased attention should be paid also to radiation exposure by inhalation.

Factors Influencing Leukocyte Adherence in Microvessels

1977 ◽  
Vol 38 (04) ◽  
pp. 0823-0830 ◽  
Author(s):  
Mayrovttz N. Harvey ◽  
Wiedeman P. Mary ◽  
Ronald F. Tuma
Keyword(s):  
Blood Flow ◽  
Shear Stress ◽  
Tissue Injury ◽  
Threshold Value ◽  
In Vivo Studies ◽  
Leukocyte Adherence ◽  
Rolling Velocity ◽  
Subsequent Behavior ◽  
Flow Stasis

SummaryIn vivo studies of the microcirculation of an untraumatized and unanesthetized animal preparation has shown that leukocyte adherence to vascular endothelium is an extremely rare occurrence. Induction of leukocyte adherence can be produced in a variety of ways including direct trauma to the vessels, remote tissue injury via laser irradiation, and denuding the epithelium overlying the observed vessels. The role of blood flow and local hemodynamics on the leukocyte adherence process is quite complex and still not fully understood. From the results reported it may be concluded that blood flow stasis will not produce leukocyte adherence but will augment pre-existing adherence. Studies using 2 quantitative measures of adherence, leukocyte flux and leukocyte velocity have shown these parameters to be affected differently by local hemodynamics. Initial adherence appears to be critically dependent on the magnitude of the blood shear stress at the vessel wall as evidenced by the lack of observable leukocyte flux above some threshold value. Subsequent behavior of the leukocytes as characterized by their average rolling velocity shows no apparent relationship to shear stress but, for low velocities, may be related to the linear blood velocity.

QSAR modeling for predicting carcinogenic potency of nitroso-compounds using 0D-2D molecular descriptors

2007 ◽  
Author(s):  
Maykel González ◽  
Aliuska Helguera ◽  
M. Natália Cordeiro ◽  
Miguel Cabrera Pérez ◽  
Reinaldo Ruiz ◽  
...  
Keyword(s):  
Molecular Descriptors ◽  
Nitroso Compounds ◽  
Qsar Modeling ◽  
Carcinogenic Potency

Path Tracking Controller Design of Automatic Guided Vehicle Based on Four-Wheeled Omnidirectional Motion Model

2020 ◽  
Vol 17 (2) ◽  
pp. 7996-8010
Author(s):  
X. Wu ◽  
Y. Yang
Keyword(s):  
Control System ◽  
Fuzzy Controller ◽  
Controller Design ◽  
Threshold Value ◽  
Position Angle ◽  
Path Tracking ◽  
Global Coordinate System ◽  
Automatic Guided Vehicle ◽  
Input Variables ◽  
Industrial Pc

This paper presents a new design of omnidirectional automatic guided vehicle based on a hub motor, and proposes a joint controller for path tracking. The proposed controller includes two parts: a fuzzy controller and a multi-step predictive optimal controller. Firstly, based on various steering conditions, the kinematics model of the whole vehicle and the pose (position, angle) model in the global coordinate system are introduced. Secondly, based on the modeling, the joint controller is designed. Lateral deviation and course deviation are used as the input variables of the control system, and the threshold value is switched according to the value of the input variable to realise the correction of the large range of posture deviation. Finally, the joint controller is implemented by using the industrial PC and the self-developed control system based on the Freescale minimum system. Path tracking experiments were made under the straight and circular paths to test the ability of the joint controller for reducing the pose deviation. The experimental results show that the designed guided vehicle has excellent ability to path tracking, which meets the design goals.

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