bluuebunny/crossref_metadata_2025_split huggingface dataset:
Relaxation in systems with exponential or Gaussian distributions of activation energies
Authors: Macdonald J. Ross 
Published: July 2002

New expressions are presented, simplified, and discussed for the small-signal-frequency response of systems involving distributions of activation energies with either exponential or Gaussian probability densities. The results involve the possibility of separate but related thermal activation of energy-storage and energy-loss processes, and apply to the response of both dielectric and conductive systems. Response with a Gaussian distribution of activation energies (GDAE) may be either symmetric or asymmetric in log frequency, and typical GDAE responses are compared with those associated with several exponential distributions of activation-energy (EDAE) models, using complex nonlinear least-squares fitting. The GDAE model does not lead to the frequently observed fractional-exponent power-law response in time or frequency as does the EDAE; thus, the GDAE cannot fit any EDAE response well which involves an appreciable range of such behavior, but it is found that, conversely, the general EDAE model can often fit a GDAE response very well over
a wide frequency range. Recent (KBr)0.5(KCN)0.5 dielectric data covering a range from T=13.7 to 34.7 K are analyzed with the Cole–Cole, EDAE, and GDAE models, and the GDAE is found to yield the best overall fits. The results of the GDAE fits are analyzed in detail to illustrate the application of the GDAE model to real data. Contrary to the conclusions of an earlier analysis of the same data using an idealized, symmetric, and approximate GDAE model, we find that much of the data are better fit by a somewhat asymmetric, exact GDAE model which may involve a temperature-independent, finite-width Gaussian probability density. The present analysis suggests an alternative to the earlier results and suggestions that the width of the probability-density distribution increases with decreasing temperature and that the activation energies or barrier heights themselves depend linearly on temperature. The present data fit yield estimates of the lower limit of the temperature independent distribution of activation energies E0 and of the more or less central activation energy E1, but only set a lower limit for the value of the maximum activation energy of the distribution, E∞. There is some evidence from the fitting that there may be a glasslike transition below about 4 K, but other effects outside the GDAE model may intervene before that temperature region is reached.
Evolution of molecular dissociation through an electronic curve crossing: Polarized emission spectroscopy of CH3I at 266 nm
Authors: Lao K. Q. , Person M. D. , Xayariboun P. , Butler L. J. 
Published: July 2002

We present a study of the dissociation of CH3I on coupled repulsive electronic potential energy surfaces by the technique of polarized emission spectroscopy. We excite CH3I at 266 nm and disperse the photons emitted from the dissociating molecule by both frequency and angular distribution with respect to the polarization direction of the excitation laser. We thus measure the polarization of the first 12 C–I stretching emission features, corresponding to the spectral region between 266 and 317 nm. We also obtain the rotational envelope of selected emission features in higher resolution scans and model the lineshapes with parameters derived from the polarization results. The polarization measurements show the emission into the first few low-lying C–I stretching vibrational levels is via a transition moment parallel to the absorbing one, consistent with excitation to and emission from the 3Q0(2A1) repulsive surface. Emission to higher C–I stretching overtones shows an increasing contribution from emission via a transition moment perpendicular to the absorbing one, consistent with emission from a repulsive surface of E symmetry following excitation to the 3Q0(2A1) state.
We extract from the data the fraction of photons emitted via a perpendicular transition for each of the C–I stretch emission features. The analysis includes the derivation of analytic expressions for the angular distribution of the photons, with and without integration over the rotational contour, when the detector has a finite acceptance angle. We discuss the results in relation to a simple model where photoabsorption excites the molecule to the 3Q0(2A1) repulsive surface (parallel transition moment) and amplitude develops on the 1Q1(3E) repulsive surface as the molecule dissociates through a curve crossing. The changes in amplitude of the molecular wavefunction on the A1 vs the E repulsive surfaces during dissociation is thus probed. We outline a crude classical quasidiatomic approximation for roughly extracting from our data the electronic energy at which the ‘‘curve crossing’’ occurs. This derived energy is compared to that given in model and ab initio calculations of the excited electronic potential energy surfaces. Finally, we discuss the results in relation to the simple quasidiatomic Landau–Zener crossing model utilized by other workers, a model which does not fully explain the collection of experimental results over the last decade on the iodoalkane curve crossing.
Trajectory study of Si4 formation and decay and of exchange and abstraction reactions in Si+Si3 collisions
Authors: Kay Ronald D. , Raff Lionel M. , Thompson Donald L. 
Published: July 2002

The formation and subsequent decay of Si4 complexes as well as the direct exchange and abstraction processes in Si+Si3 collisions have been studied using quasiclassical trajectories on a new global Si4 potential energy surface fitted to available experimental and ab initio data, and on Bolding and Andersen’s (BA) recently formulated silicon potential for arbitrary cluster sizes. Cross sections for Si4 formation, σf(Et), were computed as a function of initial relative translational energy Et over the range 0.01 to 4.0 eV, with the Si3 internal energy described by the Boltzmann distribution at 800 K. The cross section was found to peak sharply near Et=0, as expected, and to fall off linearly at high energy. An analytical expression for kf(T), the thermal rate constant for Si4 formation, was found by averaging σf(Et) over the Maxwell–Boltzmann distribution for Et.
The analytical values of kf(T) lie between 6×1014 and 8×1014 cm3/mol s for the range 800–1500 K, and are in excellent accord with trajectory calculations of kf at 800 and 1200 K. Unimolecular dissociation rate constants for Si4, kd, were calculated as a function of Et over the 0.4 to 4.0 eV. The values of kd are well described by the RRK expression, with a value of 4.67 for the effective number of vibrational modes. Averaging the dissociation rate constant over the Maxwell–Boltzmann distribution yields an average Si4 lifetime of 413 ps at 800 K, which is not long enough for a stabilizing collision to occur at pressures characteristic of low-pressure CVD experiments. The direct exchange reaction is found to be unimportant for Et less than 1 eV, since for lower relative energies essentially all reactions proceed indirectly via Si4 complex formation. Direct atomic abstraction is energetically forbidden, on average, for Et less than 0.9 eV, and is unlikely for Et less than 2 eV. At higher energies, the end-atom exchange and abstraction channels, which are statistically favored over the apex-atom channels, are dynamically favored as well.
When exchange or abstraction proceeds indirectly via an Si4 intermediate, the distinction between apex-atom, end-atom, and no-reaction channels is lost. Both the direct and indirect pathways leave a large fraction of the energy and angular momentum in the reaction products. Cross sections for Si4 formation on the BA surface are smaller than those on the global Si4 surface due to the cutoff function in the BA two-body potential terms; Si4 dissociation rates for total energies between 1.3 and 2 eV above threshold agree to within a factor of 2.3 or better with corresponding values for the Si4 surface.
Slit jet infrared spectroscopy of hydrogen bonded N2HF isotopomers: Rotational Rydberg–Klein–Rees analysis and H/D dependent vibrational predissociation rates
Authors: Nesbitt David J. , Lindeman Theodore G. , Farrell John T. , Lovejoy Chris M. 
Published: July 2002

High resolution IR laser direct absorption spectra in a slit jet are presented and analyzed for nitrogen (15N14N–HF, 14N15N–HF, 15N15N–HF), and deuterium (14N14N–DF) substituted N2HF isotopomers. Both 14N15N–HF and 15N14N–HF isomers are observed, indicating a sufficiently deep minimum in the hydrogen bonding potential energy surface to quench internal rotation of the N2. The vibrationally averaged stretching potentials for each substituted species are recovered from rotational Rydberg–Klein–Rees (RKR) analysis. Features of the one-dimensional (1D) potential surface such as hydrogen bond length (RH-bond), harmonic force constant (kσ), and well depth (De) are then tested for isotopic invariance by direct comparison of the different isotopomers. Agreement among the various N substituted species for HF based complexes for either vHF=0 or 1 is excellent, and provides effective 1D potentials for the stretching coordinate between 3.39 and 3.75 Å. There is a 43 cm−1 (∼10%) strengthening of the hydrogen bond upon HF vibrational excitation, as quantitatively reflected in the experimental redshifts and the shape of the RKR potentials for vHF=0 and 1.
The hydrogen bond is further strengthened by D/H isotopic substitution; this is a result of reduced vibrational averaging over DF vs HF bending motion, yielding a more linear, and hence stronger, hydrogen bond geometry. In contrast to the nearly apparatus-limited linewidths (Δνprediss∼7 MHz) observed for each of the N2HF isotopomers, the N2DF complexes yield significantly broadened lines with 73±9 MHz homogeneous linewidths due to vibrational predissociation. This tenfold increase in predissociation rates upon deuteration is in contrast to previous measurements in other HF/DF containing complexes, and indicates the importance of a near resonant vibrational channel to form N2(v=1)+DF(v=0). The energetic accessibility of this V→V channel would suggest an upper limit on the N2DF binding energy of D0≤547 cm−1, which is also consistent with upper limits on D0 from the rotational RKR analysis.
Summation-free expression for some special Clebsch–Gordan coefficients
Authors: Rashid M. A. 
Published: July 2002

The known general formula for the Clebsch–Gordan coefficients of the three-dimensional rotation group involves one summation that results in explicit summation-free expressions for the coefficients where either one of the angular momenta is the sum of the other two or the magnetic quantum number corresponding to one of the angular momenta takes its maximum value in magnitude. By using very different techniques, explicit expressions for the coefficients 〈 j1, 0;  j2, 0‖ j, 0〉, 〈 j1, (1)/(2) ; j2, − (1)/(2) ‖ j, 0〉 are also obtained where the integral or half-integral nature of the  j’s is indicated by the magnetic quantum number involved. Here the expressions depend upon whether  j1+ j2+ j is an even or an odd integer. For these coefficients, the magnetic quantum numbers involved take their minimum value in magnitude. By using the recursion relation for the coefficients of the form 〈 j1, m,  j2, −m, ‖ j, 0〉, these coefficients can be calculated in terms of the above known ones provided the explicit value of the coefficient 〈 j1, 1;  j2, −1‖ j, 0〉 is known, where  j1+ j2+ j is an odd integer. (The recursion relation for these coefficients in terms of 〈 j1, 0;  j2, −1‖ j, 0〉 becomes a triviality since 〈 j1, 0;  j2, 0‖ j, 0〉 vanishes when  j1+ j2+ j is an odd integer.)
The main purpose of this paper is to give an explicit expression for the coefficients 〈 j1, 1;  j2, −1‖ j, 0〉, where  j1+ j2+ j is an odd integer. This expression is obtained by using a complicated transformation between hypergeometric functions, which seems to have been neglected so far. For the coefficients where the magnetic quantum numbers have their minimum value in magnitude, this transformed expression becomes summation-free and the explicit values of the three already known coefficients and the fourth so far unknown are obtained. Further study of this transformation may be useful on its own because it provides a link between very different types of expressions. For completeness, explicit expressions for the coefficient 〈 j1, 1;  j2, −1‖ j, 0〉, where  j1+ j2+ j is an even integer, and of 〈 j1, 1;  j2, 1‖ j, 2〉 and 〈 j1, (1)/(2) ;  j2, − (1)/(2) ‖ j, 0〉, where  j1+ j2+ j is an even or an odd integer, are given.
Caspase Requirement for Neuronal Apoptosis and Neurodegeneration
Authors: Nicotera Pierluigi 
Published: July 2002

AbstractThe execution of the apoptotic programme involves a relatively few pathways that converge on activation of the caspase family of proteases. However, increasing evidence indicates that apoptoticlike features can be found also when cells are treated with inhibitors of caspases. This has posed questions as to whether death with apoptotic features can still occur in a caspase‐independent way, and whether caspase inhibitors may then be used to prevent excess apoptosis in disease. Metabolic defects, loss of neuronal connectivity and cell loss characterise several neurodegenerative diseases. Targeting excessive cell demise may be one therapeutic strategy. However, loss of connectivity and neurite regression may not be part of the apoptotic programme, and degenerating neurons might use multiple execution pathways. In addition, metabolic defects leading to ATP depletion can preclude caspase activation and consequently switch execution of cell death towards necrosis. The possibility of inhibiting apoptosis as strategy to treat neurodegenerative disease is discussed in this review.
Segmentation of yeast DNA using hidden Markov models
Authors: Peshkin Leonid , S.Gelfand Mikhail 
Published: July 2002

Abstract
Motivation: Compositionally homogeneous segments of genomic DNA often correspond to meaningful biological units. Simple sliding window analysis is usually insufficient for compositional segmentation of natural sequences. Hidden Markov models (HMM) with a small number of states are a natural language for description of compositional properties of chromosome-size DNA sequences.
Results: The algorithms were applied to yeast Saccharomyces cerevisiae chromosomes (YC) I, III, IV, VI and IX. The optimal number of HMM states is found to be four. The optimal four-state HMMs for all chromosomes are very similar, as well as the reconstructed segmentations. In most cases the models with k + 1 states are obtained by ‘splitting’ one of the states in the model with k states, and the corresponding increase of the level of detail in segmentation. The high AT states usually correspond to intergenic regions. We also explore the model’s likelihood landscape and analyze the dynamics of the optimization process, thus addressing the problem of reliability of the obtained optima and efficiency of the algorithms.
Availability: The system is available on request from the first author.
Contact: ldp@cs.brown.edu
On the complexity measures of genetic sequences
Authors: D.Gusev Vladimir , A.Nemytikova Lubov , A.Chuzhanova Nadia 
Published: July 2002

Abstract
Motivation: It is well known that the regulatory regions of genomes are highly repetitive. They are rich in direct, symmetric and complemented repeats, and there is no doubt about the functional significance of these repeats. Among known measures of complexity, the Ziv–Lempel complexity measure reflects most adequately repeats occurring in the text. But this measure does not take into account isomorphic repeats. By isomorphic repeats we mean fragments that are identical (or symmetric) modulo some permutation of the alphabet letters.
Results: In this paper, two complexity measures of symbolic sequences are proposed that generalize the Ziv–Lempel complexity measure by taking into account any isomorphic repeats in the text (rather than just direct repeats as in Ziv–Lempel). The first of them, the complexity vector, is designed for small alphabets such as the alphabet of nucleotides. The second is based on a search for the longest isomorphic fragment in the history of sequence synthesis and can be used for alphabets of arbitrary cardinality. These measures have been used for recognition of structural regularities in DNA sequences. Some interesting structures related to the regulatory region of the human growth hormone are reported.
Availability: Available on request from the authors.
Contact: gusev@math.nsc.ru; nadia.chuzhanova@cs.cf.ac.uk
GPI‐anchored proteins: now you see ’em, now you don’t
Authors: BÜTIKOFER PETER , MALHERBE TATIANA , BOSCHUNG MONIKA , RODITI ISABEL 
Published: July 2002

ABSTRACTMany cell surface proteins are attached to membranes via covalent glycosylphosphatidylinositol (GPI) anchors that are posttranslationally linked to the carboxy‐terminus of the protein. Removal of the GPI lipid moieties by enzymes such as GPI‐specific phospholipases or by chemical treatments generates a soluble form of the protein that no longer associates with lipid bilayers. We have found that the removal of lipid moieties from the anchor can also have a second, unexpected effect on the antigenicity of a variety of GPI‐anchored surface molecules, suggesting that they undergo major conformational changes. Several antibodies raised against GPI‐anchored proteins from protozoa and mammalian cells were no longer capable of binding the corresponding antigens once the lipid moieties had been removed. Conversely, antibodies raised against soluble (delipidated) forms reacted poorly with intact GPI‐anchored proteins, but showed enhanced binding after treatment with phospholipases. In the light of these findings, we have reevaluated a number of publications on GPI‐anchored proteins. Many of the results are best explained by lipid‐dependent changes in antigenicity, indicating this might be a widespread phenomenon. Since many pathogen surface proteins are GPI‐anchored, researchers should be aware that the presence or absence of the GPI lipid moieties may have a major impact on the host immune response to infection or vaccination.—Bütikofer, P., Malherbe, T., Boschung, M., Roditi, I. GPI‐anchored proteins: now you see 'em, now you don't. FASEB J. 15, 545–548 (2001)
Travel Time Reliability
Authors: Karr Alan F. 
Published: May 2022

Abstract
Travel time reliability connotes variability in travel times on roadway segments and routes, often measured by extreme percentiles of distributions derived from multiple data sources. Variability results from changes in demand (e.g., rush hours and special events) or supply (e.g., weather, work zones, and traffic signals). Estimates of travel time reliability support informed departure decisions and route selection by drivers as well as interventions and design choices by system operators.
Organic Ion Template‐Guided Solution Growth of Ultrathin Bismuth Oxyselenide with Tunable Electronic Properties for Optoelectronic Applications
Authors: Dang Le‐Yang , Liu Mingqiang , Wang Gui‐Gen , Zhao Da‐Qiang , Han Jie‐Cai , Zhu Jia‐Qi , Liu Zheng 
Published: May 2022

Abstract2D Bi2O2Se has recently attracted widespread research interest due to its high electron mobility and good air stability with tunable bandgap. However, the direct and controllable growth of large‐size, high‐quality ultrathin Bi2O2Se with tunable electronic properties remains a great challenge. Here, an organic ion template‐guided solution growth method, is developed using water as a solvent to efficiently obtain high‐quality 2D Bi2O2Se. Significantly, the thicknesses and morphologies of 2D Bi2OxSe with various oxygen deficiencies; are also achieved. Optical spectroscopic results indicate that oxygen defects can dramatically tune the electronic properties of Bi2O2Se, such as work function, band gap, and energy‐band positions. As a result, the optimized Bi2O2Se devices exhibit a high photoresponsivity of 842.91 A W−1, photo‐detectivity of 8.18 × 1012 Jones under 532 nm laser, and electron mobility of 334.7 cm2 V−1 s−1. This work proposes a new green solution method to synthesize large‐sized, high‐quality Bi2O2Se with tunable electronic structures that can be extended for various applications and provides a new possibility of transfer‐free large‐scale device manufacturing.
Sulfone‐Incorporated Multi‐Resonance TADF Emitter for High‐Performance Narrowband Blue OLEDs with EQE of 32%
Authors: Hua Tao , Miao Jingsheng , Xia Han , Huang Zhongyan , Cao Xiaosong , Li Nengquan , Yang Chuluo 
Published: May 2022

AbstractThe blue multi‐resonance thermally activated delayed fluorescence materials, simultaneously realizing narrow full‐width at half‐maximum, high external quantum efficiency (EQE), and low efficiency roll‐off, remains a formidable challenge. Herein, three novel emitters, namely PTZBN1, PTZBN2, and PTZBN3, are designed by gradual peripheral modification in boron/nitrogen (B/N) embedded polycyclic skeleton, which exhibit progressively hypsochromic‐shifted emission from 490 nm (PTZBN1) to 468 nm (PTZBN3) with photoluminescence quantum yields up to 98%. In particular, the incorporation of sulfone unit in the boron/nitrogen (B/N) embedded polycyclic skeleton provides a simple but effective tactic for narrowband blue emission. The organic light‐emitting diodes based on PTZBN2 achieve one of the‐state‐of‐the‐art EQEs of 34.8% with electroluminescence (EL) peak at 478 nm. Impressively, PTZBN3‐based device exhibits not only a high maximum EQE of 32.0% with EL peak at 468 nm, but also low efficiency roll‐off.
Integrated Memory Devices Based on 2D Materials
Authors: Xue Fei , Zhang Chenhui , Ma Yinchang , Wen Yan , He Xin , Yu Bin , Zhang Xixiang 
Published: May 2022

AbstractWith the advent of the Internet of Things and big data, massive data must be rapidly processed and stored within a short timeframe. This imposes stringent requirements on memory hardware implementation in terms of operation speed, energy consumption, and integration density. To fulfill these demands, 2D materials, which are excellent electronic building blocks, provide numerous possibilities for developing advanced memory device arrays with high performance, smart computing architectures, and desirable downscaling. Over the past few years, 2D‐material‐based memory‐device arrays with different working mechanisms, including defects, filaments, charges, ferroelectricity, and spins, have been increasingly developed. These arrays can be used to implement brain‐inspired computing or sensing with extraordinary performance, architectures, and functionalities. Here, recent research into integrated, state‐of‐the‐art memory devices made from 2D materials, as well as their implications for brain‐inspired computing are surveyed. The existing challenges at the array level are discussed, and the scope for future research is presented.