Search results for "force"
showing 10 items of 3423 documents
Ancient human genomes suggest three ancestral populations for present-day Europeans
2014
We sequenced the genomes of a ∼7,000-year-old farmer from Germany and eight ∼8,000-year-old hunter-gatherers from Luxembourg and Sweden. We analysed these and other ancient genomes1,2,3,4 with 2,345 contemporary humans to show that most present-day Europeans derive from at least three highly differentiated populations: west European hunter-gatherers, who contributed ancestry to all Europeans but not to Near Easterners; ancient north Eurasians related to Upper Palaeolithic Siberians3, who contributed to both Europeans and Near Easterners; and early European farmers, who were mainly of Near Eastern origin but also harboured west European hunter-gatherer related ancestry. We model these popula…
Exploiting the Exiles: Soviet Émigrés in U.S. Cold War Strategy
2012
This article discusses the abortive U.S. government effort to organize Soviet émigrés after World War II. After years of a lack of interest on the part of both the United States and the Soviet Union, Soviet émigrés and émigré politics came to the fore with the onset of the Cold War. The U.S. government sought to use émigrés in political and psychological warfare against the Soviet bloc. The many studies that have looked at Cold War-era psychological warfare have largely ignored U.S. plans to enlist Soviet émigrés on the West's behalf. Attempts to create a political forum for anti-Bolshevik Soviet émigrés were broader than have been understood thus far, revealing important information about…
Anomalous behaviour of periodic domain structure in Gd-doped LiNbO3single crystals
2007
Atomic force microscopy studies of etching patterns, stability of regular domain structure, and anomalies of electrical characteristics in the 300 - 385 K range of a series of Gddoped lithium niobate single crystals grown under equal conditions are reported.
‘The Iraq War Momentum’ in the Struggle on the Powers of the US Congress
2019
How parliaments and legislatures participate in war-making has raised interest among researchers from different disciplines, including constitutional law and political science. While war powers are usually considered to be included in the field of the executive branch, parliaments have played an increasingly relevant role as more democratic decision-making in both normal and exceptional times has gained prominence. The comparative aspect to examine war powers between parliaments or between the branches of government is often adopted to describe the authority and legitimacy of these powers. The US Congress is considered to have strong war powers on paper compared to parliaments in other libe…
Development of a Simulator for Prototyping Reinforcement Learning-Based Autonomous Cars
2022
Autonomous driving is a research field that has received attention in recent years, with increasing applications of reinforcement learning (RL) algorithms. It is impractical to train an autonomous vehicle thoroughly in the physical space, i.e., the so-called ’real world’; therefore, simulators are used in almost all training of autonomous driving algorithms. There are numerous autonomous driving simulators, very few of which are specifically targeted at RL. RL-based cars are challenging due to the variety of reward functions available. There is a lack of simulators addressing many central RL research tasks within autonomous driving, such as scene understanding, localization and mapping, pla…
Gold-Catalyzed Intramolecular Hydroamination of o-Alkynylbenzyl Carbamates: A Route to Chiral Fluorinated Isoindoline and Isoquinoline Derivatives
2013
Enantiomerically pure fluorinated isoindoline and dihydroisoquinoline scaffolds have been prepared through a diastereoselective addition of fluorinated nucleophiles to Ellman’s N-(tert-butanesulfinyl)imines followed by a sequence of Sonogashira cross-coupling/gold(I)-catalyzed cycloisomerization of the corresponding carbamate. A more favored 5-exo-dig mechanism was observed mainly due to an electronic effect of the fluorinated group.
Chloride–hydrogen interactions of picolinic, nicotinic and isonicotinic acid chloride hydrochlorides in the crystalline state
2003
The crystal structures of the three isomers of the chemically labile pyridinecarboxylic acid chloride hydrochlorides were analyzed in order to study the weak interactions of the chloride anion with hydrogens. The chloride anions in the crystal structure of 1a have a slightly distorted square-planar interaction sphere with four hydrogens in the equatorial plane (plane of the molecule) with Cl−⋯H distances varying from 2.041(1) A [NH+⋯Cl−] to 2.933(1) A [CH⋯Cl−]. Nicotinic and isonicotinic acid chloride hydrochloride 1b and 1c show that chloride anion has a crucial role in the formation of bridged dimeric structures. The crystal lattices of 1b and 1c manifest similar herring-bone packing patt…
NMR crystallography of 2-Acylamino-6-[1H]pyridones: solid state NMR, GIPAW computational, and single crystal X-ray diffraction studies
2011
Abstract 2-Acylamino-6-[1H]-pyridones [acyl = RCO, where R = methyl (1), ethyl (2), iso-propyl (3), tert-butyl (4), and 1-adamantyl (5)] have been synthesized and characterized by NMR spectroscopy. From three congeners, 2, 3 and 5, also single crystal X-ray structures have been solved. For these derivatives GIPAW calculations acts as a “bridge” between solid-state NMR data and calculated chemical shifts based on X-ray determined geometry. In crystals all three compounds exist as pyridone tautomers possessing similar six-membered ring structure stabilized by intramolecular C O⋯HN hydrogen bond. Theoretical GIPAW calculated and experimental 13C and 15N CPMAS NMR shifts are in excellent agreem…
NMR spectral and X-ray structural investigation of 1,3-bis(2-quinolyl)-2-(p-chlorophenyl)-2-propanol
2000
Abstract 1,3-Bis(2-quinolyl)-2-(p-chlorophenyl)-2-propanol (BQCP) has been prepared and characterised by 1H, 13C, 15N NMR spectral and X-ray structural parameters. The methylene protons of BQCP are diastereotopic in solution (CDCl3) as revealed by 1H NMR. In crystalline state there exists an intramolecular hydrogen bond O–H⋯N with one of two nitrogen atoms in BQCP. Variable temperature 1H NMR and PFG 1H, 15N HMBC runs show that in solution BQCP shows C2v-symmetry (both CH2-2-quinolyl fragments are equivalent) in NMR-time scale due to a fast exchange of the hydrogen bond from one nitrogen to the other even at 223 K.
Reversible hydrogen bond network dynamics: molecular dynamics simulations of calix[4]arene-catenanes.
2011
We present detailed molecular dynamics (MD) simulations of mechanically interlocked calix[4]arene-catenanes under external force. Single-molecule force spectroscopy experiments revealed that the separation of dimers with two aliphatic loops results in reversible hydrogen bond breakage through an intermediate in a triple-well potential, while the tetra-loop species separates in a one-step manner (Janke, M.; et al. Nat. Nanotechnol. 2009, 4, 225). MD simulations show that calix[4]arenes interlocked by four loops (1) display a complete restructuring of the hydrogen bond network under mechanical force. All hydrogen bonds of the closed structure open, and new ones are formed in the extended stru…