Covalent Bonding: The Fundamental Role of the Kinetic Energy

2013 ◽  
Vol 117 (33) ◽  
pp. 7946-7958 ◽  
Author(s):  
George B Bacskay ◽  
Sture Nordholm
Keyword(s):  
Kinetic Energy ◽  
Covalent Bonding

scholarly journals The Basics of Covalent Bonding in Terms of Energy and Dynamics

Molecules ◽  
2020 ◽  
Vol 25 (11) ◽  
pp. 2667 ◽  
Author(s):  
Sture Nordholm ◽  
George B. Bacskay
Keyword(s):  
Kinetic Energy ◽  
Covalent Bond ◽  
Covalent Bonding ◽  
Bonding Mechanism ◽  
Physical Origin ◽  
Bonding Analysis ◽  
Molecule Formation ◽  
The Subject ◽  
Modern Form

We address the paradoxical fact that the concept of a covalent bond, a cornerstone of chemistry which is well resolved computationally by the methods of quantum chemistry, is still the subject of debate, disagreement, and ignorance with respect to its physical origin. Our aim here is to unify two seemingly different explanations: one in terms of energy, the other dynamics. We summarize the mechanistic bonding models and the debate over the last 100 years, with specific applications to the simplest molecules: H2+ and H2. In particular, we focus on the bonding analysis of Hellmann (1933) that was brought into modern form by Ruedenberg (from 1962 on). We and many others have helped verify the validity of the Hellmann–Ruedenberg proposal that a decrease in kinetic energy associated with interatomic delocalization of electron motion is the key to covalent bonding but contrary views, confusion or lack of understanding still abound. In order to resolve this impasse we show that quantum mechanics affords us a complementary dynamical perspective on the bonding mechanism, which agrees with that of Hellmann and Ruedenberg, while providing a direct and unifying view of atomic reactivity, molecule formation and the basic role of the kinetic energy, as well as the important but secondary role of electrostatics, in covalent bonding.

scholarly journals The Role of Discs in the Collapse and Fragmentation of Prestellar Cores

2016 ◽  
Vol 33 ◽  
Author(s):  
O. Lomax ◽  
A. P. Whitworth ◽  
D. A. Hubber
Keyword(s):  
Kinetic Energy ◽  
Smoothed Particle Hydrodynamics ◽  
Low Mass Stars ◽  
Gravitational Instabilities ◽  
Disc Material ◽  
Prestellar Cores ◽  
Particle Hydrodynamics ◽  
Smoothed Particle ◽  
Low Mass

AbstractDisc fragmentation provides an important mechanism for producing low-mass stars in prestellar cores. Here, we describe smoothed particle hydrodynamics simulations which show how populations of prestellar cores evolve into stars. We find the observed masses and multiplicities of stars can be recovered under certain conditions.First, protostellar feedback from a star must be episodic. The continuous accretion of disc material on to a central protostar results in local temperatures which are too high for disc fragmentation. If, however, the accretion occurs in intense outbursts, separated by a downtime of ~ 104yr, gravitational instabilities can develop and the disc can fragment.Second, a significant amount of the cores’ internal kinetic energy should be in solenoidal turbulent modes. Cores with less than a third of their kinetic energy in solenoidal modes have insufficient angular momentum to form fragmenting discs. In the absence of discs, cores can fragment but results in a top-heavy distribution of masses with very few low-mass objects.

scholarly journals EDEM2 stably disulfide-bonded to TXNDC11 catalyzes the first mannose trimming step in mammalian glycoprotein ERAD

eLife ◽  
2020 ◽  
Vol 9 ◽  
Author(s):  
Ginto George ◽  
Satoshi Ninagawa ◽  
Hirokazu Yagi ◽  
Taiki Saito ◽  
Tokiro Ishikawa ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Gene Knockout ◽  
Covalent Bonding ◽  
Cxxc Motif ◽  
Endoplasmic Reticulum Associated Degradation ◽  
Endoplasmic Reticulum Protein ◽  
Hct116 Cells

Sequential mannose trimming of N-glycan (Man9GlcNAc2 -> Man8GlcNAc2 -> Man7GlcNAc2) facilitates endoplasmic reticulum-associated degradation of misfolded glycoproteins (gpERAD). Our gene knockout experiments in human HCT116 cells have revealed that EDEM2 is required for the first step. However, it was previously shown that purified EDEM2 exhibited no α1,2-mannosidase activity toward Man9GlcNAc2 in vitro. Here, we found that EDEM2 was stably disulfide-bonded to TXNDC11, an endoplasmic reticulum protein containing five thioredoxin (Trx)-like domains. C558 present outside of the mannosidase homology domain of EDEM2 was linked to C692 in Trx5, which solely contains the CXXC motif in TXNDC11. This covalent bonding was essential for mannose trimming and subsequent gpERAD in HCT116 cells. Furthermore, EDEM2-TXNDC11 complex purified from transfected HCT116 cells converted Man9GlcNAc2 to Man8GlcNAc2(isomerB) in vitro. Our results establish the role of EDEM2 as an initiator of gpERAD, and represent the first clear demonstration of in vitro mannosidase activity of EDEM family proteins.

Holism: mental and semantic

2018 ◽  
Author(s):  
Ned Block
Keyword(s):  
Kinetic Energy ◽  
Real Difference ◽  
Theoretical Terms ◽  
Inferential Role ◽  
The World ◽  
Energy And Momentum ◽  
Small Parts ◽  
The Web ◽  
Belief Content

Mental (or semantic) holism is the doctrine that the identity of a belief content (or the meaning of a sentence that expresses it) is determined by its place in the web of beliefs or sentences comprising a whole theory or group of theories. It can be contrasted with two other views: atomism and molecularism. Molecularism characterizes meaning and content in terms of relatively small parts of the web in a way that allows many different theories to share those parts. For example, the meaning of ‘chase’ might be said by a molecularist to be ‘try to catch’. Atomism characterizes meaning and content in terms of none of the web; it says that sentences and beliefs have meaning or content independently of their relations to other sentences or beliefs. One major motivation for holism has come from reflections on the natures of confirmation and learning. As Quine observed, claims about the world are confirmed not individually but only in conjunction with theories of which they are a part. And, typically, one cannot come to understand scientific claims without understanding a significant chunk of the theory of which they are a part. For example, in learning the Newtonian concepts of ‘force’, ‘mass’, ‘kinetic energy’ and ‘momentum’, one does not learn any definitions of these terms in terms that are understood beforehand, for there are no such definitions. Rather, these theoretical terms are all learned together in conjunction with procedures for solving problems. The major problem with holism is that it threatens to make generalization in psychology virtually impossible. If the content of any state depends on all others, it would be extremely unlikely that any two believers would ever share a state with the same content. Moreover, holism would appear to conflict with our ordinary conception of reasoning. What sentences one accepts influences what one infers. If I accept a sentence and then later reject it, I thereby change the inferential role of that sentence, so the meaning of what I accept would not be the same as the meaning of what I later reject. But then it would be difficult to understand on this view how one could rationally – or even irrationally! – change one’s mind. And agreement and translation are also problematic for much the same reason. Holists have responded (1) by proposing that we should think not in terms of ‘same/different’ meaning but in terms of a gradient of similarity of meaning, (2) by proposing ‘two-factor’ theories, or (3) by simply accepting the consequence that there is no real difference between changing meanings and changing beliefs.

scholarly journals On the Role of Asymmetric Convective Bursts to the Problem of Hurricane Intensification: Radiation of Vortex Rossby Waves and Wave–Mean Flow Interactions

2014 ◽  
Vol 71 (6) ◽  
pp. 2057-2077 ◽  
Author(s):  
Konstantinos Menelaou ◽  
M. K. Yau
Keyword(s):  
Kinetic Energy ◽  
Thermal Anomaly ◽  
Eddy Kinetic Energy ◽  
Intensity Change ◽  
Mean Flow ◽  
Symmetric Flow ◽  
Thermal Forcing ◽  
Sensitivity Experiments ◽  
Flow Interactions

Abstract The role of asymmetric convection to the intensity change of a weak vortex is investigated with the aid of a “dry” thermally forced model. Numerical experiments are conducted, starting with a weak vortex forced by a localized thermal anomaly. The concept of wave activity, the Eliassen–Palm flux, and eddy kinetic energy are then applied to identify the nature of the dominant generated waves and to diagnose their kinematics, structure, and impact on the primary vortex. The physical reasons for which disagreements with previous studies exist are also investigated utilizing the governing equation for potential vorticity (PV) perturbations and a number of sensitivity experiments. From the control experiment, it is found that the response of the vortex is dominated by the radiation of a damped sheared vortex Rossby wave (VRW) that acts to accelerate the symmetric flow through the transport of angular momentum. An increase of the kinetic energy of the symmetric flow by the VRW is shown also from the eddy kinetic energy budget. Additional tests performed on the structure and the magnitude of the initial thermal forcing confirm the robustness of the results and emphasize the significance of the wave–mean flow interaction to the intensification process. From the sensitivity experiments, it is found that for a localized thermal anomaly, regardless of the baroclinicity of the vortex and the radial and vertical gradients of the thermal forcing, the resultant PV perturbation follows a damping behavior, thus suggesting that deceleration of the vortex should not be expected.

The influence of entropy fluctuations on the interaction of turbulence with a shock wave

1997 ◽  
Vol 334 ◽  
pp. 353-379 ◽  
Author(s):  
KRISHNAN MAHESH ◽  
SANJIVA K. LELE ◽  
PARVIZ MOIN
Keyword(s):  
Numerical Simulation ◽  
Shock Wave ◽  
Kinetic Energy ◽  
Direct Numerical Simulation ◽  
Scaling Law ◽  
Linear Analysis ◽  
Turbulent Field ◽  
Bulk Compression ◽  
Baroclinic Torque

Direct numerical simulation and inviscid linear analysis are used to study the interaction of a normal shock wave with an isotropic turbulent field of vorticity and entropy fluctuations. The role of the upstream entropy fluctuations is emphasized. The upstream correlation between the vorticity and entropy fluctuations is shown to strongly influence the evolution of the turbulence across the shock. Negative upstream correlation between u′ and T′ is seen to enhance the amplification of the turbulence kinetic energy, vorticity and thermodynamic fluctuations across the shock wave. Positive upstream correlation has a suppressing effect. An explanation based on the relative effects of bulk compression and baroclinic torque is proposed, and a scaling law is derived for the evolution of vorticity fluctuations across the shock. The validity of Morkovin's hypothesis across a shock wave is examined. Linear analysis is used to suggest that shock-front oscillation would invalidate the relation between urms and Trms, as expressed by the hypothesis.

Role of the implosion kinetic energy in determining the kilovolt x-ray emission from aluminum-wire-array implosions

1991 ◽  
Vol 44 (10) ◽  
pp. 6762-6775 ◽  
Author(s):  
C. Deeney ◽  
T. Nash ◽  
R. R. Prasad ◽  
L. Warren ◽  
K. G. Whitney ◽  
...  
Keyword(s):  
Kinetic Energy ◽  
Wire Array ◽  
Aluminum Wire ◽  
X Ray

scholarly journals Study of High-Energy Fission in Inverse Kinematics

2019 ◽  
Vol 223 ◽  
pp. 01037
Author(s):  
G. Mantovani ◽  
D. Ramos ◽  
M. Caamaño ◽  
A. Lemasson ◽  
M. Rejmund ◽  
...  
Keyword(s):  
Kinetic Energy ◽  
Excitation Energy ◽  
Shell Structure ◽  
Inverse Kinematics ◽  
High Energy ◽  
Total Kinetic Energy ◽  
High Excitation Energy ◽  
High Excitation ◽  
Shell Effects

Fission at low excitation energy, is a process in which both macroscopic and microscopic aspects are involved. Some features in the total kinetic energy and in the N/Z distributions of the fragments, commonly associated with shell effects, came out in a series of recent experiments with high excitation energy fusionfission reactions in inverse kinematics. In the latest experiment of this campaign, a study of high-energy fission and quasi-fission between a 238U beam and a series of light targets was carried out by using the aforementioned technique, in order to probe the role of the shell structure in these processes.

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