Chemische Reaktionskinematik

1968 ◽  
Vol 23 (12) ◽  
pp. 2084-2090 ◽  
Author(s):  
A. Ding ◽  
A. Henglein ◽  
D. Hyatt ◽  
K. Lacmann
Keyword(s):  
Cross Sections ◽  
Degrees Of Freedom ◽  
Forward Scattering ◽  
Small Shift ◽  
High Energies ◽  
Direct Measurements ◽  
Wide Range ◽  
Ion Energies ◽  
Low Energies ◽  
Velocity Spectra

The velocity spectra and cross sections of reactions of the type X*+D2 → XD++D (X+=Ar+, N2+, CO+) have been found to be independent of the temperature of the target gas ( — 190° to 20°C). The additional forward scattering (as compared to spectator stripping) of the product ion at high energies cannot be explained by the thermal motion of the D2 molecules. A recoil stripping mechanism is proposed. At low energies, an intermediate XD2* is postulated that lives shorter than half a period of rotation and is forward scattered but quickly equilibrates the excess energy among the vibrational degrees of freedom. The reactions of Ar+ and N2+ with CD4 can well be understood by the stripping model over a wide range of energy. At low energies, no preferential forward scattering of the product ion is found as in the corresponding reactions with D2. The strongly unsymmetric broadening of the product ion band together with a small shift to lower velocities indicate a strong interaction of the incident ion with the CD3 group at low energies. The formation of an intermediate complex XCD4+ which isotropically decays is expected at energies of a few tenth of one eV. Direct measurements at such low primary ion energies have not yet been possible.

Mass Loss of Biological Molecules in the Electron Microscope

1975 ◽  
Vol 33 ◽  
pp. 676-677 ◽  
Author(s):  
M. Isaacson ◽  
J. Langmore ◽  
M. Lamvik ◽  
P. Lin ◽  
S. Golladay ◽  
...  
Keyword(s):  
Radiation Damage ◽  
Cross Sections ◽  
Biological Molecules ◽  
Specimen Preparation ◽  
Dose Rates ◽  
Direct Measurements ◽  
Wide Range ◽  
Electron Microscopes ◽  
Preparation Techniques ◽  
Fundamental Limitation

Although present-day electron microscopes can resolve single atoms, resolution of biological specimens has usually been limited to 20 Å in large part by beam-induced specimen damage. Use of the STEM, which is potentially superior to the CTEM in both contrast and specimen radiation dose necessary to form an image, and development of new specimen preparation techniques may increase resolution somewhat, but the fundamental limitation of radiation damage will still remain. Therefore we have undertaken a study of the modes of radiation damage in electron microscopy with the hope that a better understanding of these processes may aid development of techniques to reduce their effect.We present here direct measurements of the decrease of the elastic and inelastic cross sections due to electron irradiation in the STEM. These measurements cover a wide range in dose rate from less than 10-4 amps/cm2 to 300, encompassing those dose rates found in conventional as well as high resolution scanning microscopy.

Cation transport in gaseous nitrogen: density and temperature effects

1986 ◽  
Vol 64 (4) ◽  
pp. 777-779 ◽  
Author(s):  
Toshinori Wada ◽  
Norman Gee ◽  
Gordon R. Freeman
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Temperature Effects ◽  
Cation Transport ◽  
Polarization Potential ◽  
Gaseous Nitrogen ◽  
Nitrogen Gas ◽  
High Energies ◽  
Low Energies ◽  
Body Potential

The density-normalized mobility of nμ of cations in nitrogen gas at densities up to nc = 6.7 × 1027 molecules/m3 increases with temperature. At n ≤ 5.7 × 1025 molecules/m3 and T > 250 K, the dominating ion is N4+. At lower temperatures and higher densities, relatively loosely bound clusters N4+(N2), N4+(N2)2, … form. Momentum transfer cross sections for N4+–N2 are governed at low energies by the polarization potential, and at high energies by the hard body potential. The cross section for N2+–N2 at high energies is larger than that for N4+–N2.

Chemische Reaktionskinematik

1968 ◽  
Vol 23 (12) ◽  
pp. 2090-2094 ◽  
Author(s):  
A. Ding ◽  
A. Henglein ◽  
D. Hyatt ◽  
K. Lacmann
Keyword(s):  
Degrees Of Freedom ◽  
Forward Direction ◽  
Translational Energy ◽  
Fast Process ◽  
Transition Energies ◽  
High Energies ◽  
Low Energies ◽  
Relative Kinetic ◽  
Collision Mechanism ◽  
Internal Degrees Of Freedom

The distribution of the translational energy in the forward direction has been measured for the ions resulting from the reactionsCH3OH++D2 → CH3OHD++DCH3OH++CD4 → CH3OHD++CD3at various relative kinetic energies. At high energies, spectator stripping was observed. At low energies, intermediate complexes which isotropically decay are formed. The reaction with D2 has a threshold of about 0.2 eV in the CM system. The complex that is formed at energies slightly above the threshold decays without kinetic energy of the products. At high energies, exploding complexes are formed until stripping mainly determines the collision mechanism.A simple model for D-atom transfer is proposed in which both the collision time and the resonance for energy transfer from the critical degree of freedom of the transition species into the other internal degrees of freedom are regarded. The relaxation time for the energy distribution among the degrees of freedom is estimated from the observed stripping → complex transition energies. Values of some 10-14 sec were obtained,which shows that internal energy relaxation in polyatomic species is a very fast process.

scholarly journals Odderon and pomeron as fractal dimension in pp and p̄p total cross-sections

2016 ◽  
Vol 31 (10) ◽  
pp. 1650066 ◽  
Author(s):  
F. S. Borcsik ◽  
S. D. Campos
Keyword(s):  
Fractal Dimension ◽  
Total Cross Section ◽  
Cross Section ◽  
Cross Sections ◽  
Fractal Dimensions ◽  
Total Cross Sections ◽  
High Energies ◽  
Fitting Procedure ◽  
Low Energies ◽  
Section Structure

In this paper, one presents a naive parametrization to [Formula: see text] and [Formula: see text] total cross-sections. The main goal of this parametrization is to study the possible fractal structure present in the total cross-section. The result of the fitting procedure shows two different fractal dimensions: a negative (low-energies) and a positive (high-energies). The negative fractal dimension represents the emptiness of the total cross-section structure and the positive represents the filling up process with the energy increase. Hence, the total cross-section presents a multifractal behavior. At low-energies, the odderon exchange may be associated with the negative fractal dimension and at high-energies, the pomeron may be associated with the positive fractal dimension. Therefore, the exchange of odderons and pomerons may be viewed as a transition from a less well-defined to a more well-defined internal structure, depending on the energy.

Electron Ionization Cross Sections for Atomic Subshells

2003 ◽  
Vol 9 (1) ◽  
pp. 42-53 ◽  
Author(s):  
Peter Rez
Keyword(s):  
Cross Sections ◽  
Wave Functions ◽  
Mathematical Form ◽  
Atomic Shell ◽  
Ionization Cross ◽  
X Ray ◽  
High Energies ◽  
Low Energies ◽  
Ionization Cross Sections ◽  
Selection Of

Ionization of atoms is the first step in many analytical procedures. The cross section for ionizing a particular atomic shell is essential for calculating the magnitude of analytical signals. Calculations using atomic wave functions for various shells of all elements relevant for X-ray microanalysis over a range of electron energies up to 400 keV were performed. The calculations for high energies above threshold can be considerably simplified by using the mathematical form of the Bethe ridge that dominates the scattering in this region. Corrections for exchange at low energies above threshold are incorporated in these calculations. A selection of results showing the effects of different approximations on ionization cross sections for K, L, and M shells is presented.

Understanding Conformational Entropy in Small Molecules

2020 ◽  
Author(s):  
Lucian Chan ◽  
Garrett Morris ◽  
Geoffrey Hutchison
Keyword(s):  
Small Molecules ◽  
Degrees Of Freedom ◽  
Absolute Error ◽  
Low Energy ◽  
Standard Entropy ◽  
Free Energies ◽  
Conformational Entropy ◽  
Wide Range ◽  
High Degree ◽  
Empirical Corrections

The calculation of the entropy of flexible molecules can be challenging, since the number of possible conformers grows exponentially with molecule size and many low-energy conformers may be thermally accessible. Different methods have been proposed to approximate the contribution of conformational entropy to the molecular standard entropy, including performing thermochemistry calculations with all possible stable conformations, and developing empirical corrections from experimental data. We have performed conformer sampling on over 120,000 small molecules generating some 12 million conformers, to develop models to predict conformational entropy across a wide range of molecules. Using insight into the nature of conformational disorder, our cross-validated physically-motivated statistical model can outperform common machine learning and deep learning methods, with a mean absolute error ≈4.8 J/mol•K, or under 0.4 kcal/mol at 300 K. Beyond predicting molecular entropies and free energies, the model implies a high degree of correlation between torsions in most molecules, often as- sumed to be independent. While individual dihedral rotations may have low energetic barriers, the shape and chemical functionality of most molecules necessarily correlate their torsional degrees of freedom, and hence restrict the number of low-energy conformations immensely. Our simple models capture these correlations, and advance our understanding of small molecule conformational entropy.

scholarly journals A Dynamical Study of Fusion Hindrance with Nakajima-Zwanzig Projection Method

2021 ◽  
Author(s):  
Yasuhisa Abe ◽  
David Boilley ◽  
Quentin Hourdillé ◽  
Caiwan Shen
Keyword(s):  
Cross Sections ◽  
Degrees Of Freedom ◽  
Operator Method ◽  
Initial Distribution ◽  
Physical Parameters ◽  
Relaxation Processes ◽  
Fast Variable ◽  
Dynamical Study ◽  
Injection Point ◽  
Slow Variables

Abstract A new framework is proposed for the study of collisions between very heavy ions which lead to the synthesis of Super-Heavy Elements (SHE), to address the fusion hindrance phenomenon. The dynamics of the reaction is studied in terms of collective degrees of freedom undergoing relaxation processes with different time scales. The Nakajima-Zwanzig projection operator method is employed to eliminate fast variable and derive a dynamical equation for the reduced system with only slow variables. There, the time evolution operator is renormalised and an inhomogeneous term appears, which represents a propagation of the given initial distribution. The term results in a slip to the initial values of the slow variables. We expect that gives a dynamical origin of the so-called “injection point s” introduced by Swiatecki et al in order to reproduce absolute values of measured cross sections for SHE. A formula for the slip is given in terms of physical parameters of the system, which confirms the results recently obtained with a Langevin equation, and permits us to compare various incident channels.

scholarly journals Quantum information probes of charge fractionalization in large-N gauge theories

2021 ◽  
Vol 2021 (5) ◽  
Author(s):  
Brandon S. DiNunno ◽  
Niko Jokela ◽  
Juan F. Pedraza ◽  
Arttu Pönni
Keyword(s):  
Degrees Of Freedom ◽  
Gauge Theories ◽  
Entanglement Entropy ◽  
Coarse Grained ◽  
Strongly Coupled ◽  
Information Theoretic ◽  
Large N ◽  
Wide Range ◽  
Charge Fractionalization ◽  
Electric Flux

Abstract We study in detail various information theoretic quantities with the intent of distinguishing between different charged sectors in fractionalized states of large-N gauge theories. For concreteness, we focus on a simple holographic (2 + 1)-dimensional strongly coupled electron fluid whose charged states organize themselves into fractionalized and coherent patterns at sufficiently low temperatures. However, we expect that our results are quite generic and applicable to a wide range of systems, including non-holographic. The probes we consider include the entanglement entropy, mutual information, entanglement of purification and the butterfly velocity. The latter turns out to be particularly useful, given the universal connection between momentum and charge diffusion in the vicinity of a black hole horizon. The RT surfaces used to compute the above quantities, though, are largely insensitive to the electric flux in the bulk. To address this deficiency, we propose a generalized entanglement functional that is motivated through the Iyer-Wald formalism, applied to a gravity theory coupled to a U(1) gauge field. We argue that this functional gives rise to a coarse grained measure of entanglement in the boundary theory which is obtained by tracing over (part) of the fractionalized and cohesive charge degrees of freedom. Based on the above, we construct a candidate for an entropic c-function that accounts for the existence of bulk charges. We explore some of its general properties and their significance, and discuss how it can be used to efficiently account for charged degrees of freedom across different energy scales.

scholarly journals Multiorbital singlet pairing and d + d superconductivity

2021 ◽  
Vol 6 (1) ◽  
Author(s):  
Emilian M. Nica ◽  
Qimiao Si
Keyword(s):  
Time Reversal ◽  
Heavy Fermion ◽  
Degrees Of Freedom ◽  
Spin Orbit Coupling ◽  
Spin Orbit ◽  
Matrix Structure ◽  
Spin Singlet ◽  
Low Energies ◽  
Triplet Pairing ◽  
Orbital Space

AbstractRecent experiments in multiband Fe-based and heavy-fermion superconductors have challenged the long-held dichotomy between simple s- and d-wave spin-singlet pairing states. Here, we advance several time-reversal-invariant irreducible pairings that go beyond the standard singlet functions through a matrix structure in the band/orbital space, and elucidate their naturalness in multiband systems. We consider the sτ3 multiorbital superconducting state for Fe-chalcogenide superconductors. This state, corresponding to a d + d intra- and inter-band pairing, is shown to contrast with the more familiar d + id state in a way analogous to how the B- triplet pairing phase of 3He superfluid differs from its A- phase counterpart. In addition, we construct an analog of the sτ3 pairing for the heavy-fermion superconductor CeCu2Si2, using degrees-of-freedom that incorporate spin-orbit coupling. Our results lead to the proposition that d-wave superconductors in correlated multiband systems will generically have a fully-gapped Fermi surface when they are examined at sufficiently low energies.

scholarly journals Vector boson fusion at multi-TeV muon colliders

2020 ◽  
Vol 2020 (9) ◽  
Author(s):  
Antonio Costantini ◽  
Federico De Lillo ◽  
Fabio Maltoni ◽  
Luca Mantani ◽  
Olivier Mattelaer ◽  
...  
Keyword(s):  
Cross Sections ◽  
Vector Boson ◽  
High Energy ◽  
New Physics ◽  
Vector Boson Fusion ◽  
Weak Boson ◽  
Wide Range ◽  
Lepton Colliders ◽  
Muon Colliders ◽  
New Phenomena

Abstract High-energy lepton colliders with a centre-of-mass energy in the multi-TeV range are currently considered among the most challenging and far-reaching future accelerator projects. Studies performed so far have mostly focused on the reach for new phenomena in lepton-antilepton annihilation channels. In this work we observe that starting from collider energies of a few TeV, electroweak (EW) vector boson fusion/scattering (VBF) at lepton colliders becomes the dominant production mode for all Standard Model processes relevant to studying the EW sector. In many cases we find that this also holds for new physics. We quantify the size and the growth of VBF cross sections with collider energy for a number of SM and new physics processes. By considering luminosity scenarios achievable at a muon collider, we conclude that such a machine would effectively be a “high-luminosity weak boson collider,” and subsequently offer a wide range of opportunities to precisely measure EW and Higgs couplings as well as discover new particles.

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