bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of hyperfine depolarization upon creation and detection of alignment in free-jet expansions via selective photodissociation
Authors: Yan Chun , Kummel Andrew C. 
Published: July 2002

The creation of alignment by photodissociation is a well-accepted process. When an isotropic sample of gas is subjected to a strong linearly polarized laser pulse at a frequency at which the photodissociation cross section is large, the surviving molecules are usually aligned. If the transition is parallel, μ lies along the internuclear axis (ΔΛ=0) and the surviving molecules will be peaked around M=0, while for a perpendicular transition (ΔΛ=1) the surviving molecules will be peak around M=J. Although this effect has been seen in laser cavities and in the focus of laser beams, it has not been used to create aligned pulses of gas from free-jet expansions. We present the theoretical calculations for the practical creation of alignment in short free-jet gas pulses via saturation photodissociation.
Our methodology allows the propagation of the laser light along any direction and with any polarization, the quantification of the effect of hyperfine and electron spin depolarization upon the creation of alignment, direct comparison of the degree of alignment created in parallel versus perpendicular transitions when the polarizations are set to cause M=J versus M=0 peaked distributions, experimental determination of the degree of alignment after depolarization using a second fixed frequency laser, and experimental determination of the degree of alignment prior to depolarization without the use of an additional laser. Our calculations show that hyperfine and electron spin depolarization are the limiting forces in the creation of aligned pulses of gas. These effects are most pernicious in free-jet expansions where only the lowest rotational states are populated and therefore even modest values of nuclear spin and electron spin can effect large depolarizations.
The calculations show that these depolarization effects can be effectively mitigated by three methods: (1) using molecules with small Be values, (2) limiting the free-jet expansion so the rotational temperature is above about 50 K, and (3) employing parallel photodissociation transitions (ΔΛ=0). For very cold expansions, parallel transitions are less susceptible to depolarization than perpendicular transitions (ΔΛ=1) because in parallel transitions, the low J states are selectively photodissociated.
Sub-Doppler, infrared laser spectroscopy of the propyne 2ν1 band: Evidence of z-axis Coriolis dominated intramolecular state mixing in the acetylenic CH stretch overtone
Authors: McIlroy Andrew , Nesbitt David J. , Kerstel Erik R. Th. , Pate Brooks H. , Lehmann Kevin K. , Scoles Giacinto 
Published: July 2002

The eigenstate-resolved 2ν1 (acetylenic CH stretch) absorption spectrum of propane has been observed for J′=0–11 and K=0–3 in a skimmed supersonic molecular beam using optothermal detection. Radiation near 1.5 μm was generated by a color center laser allowing spectra to be obtained with a full-width at half-maximum resolution of 6×10−4 cm−1 (18 MHz). Three distinct characteristics are observed for the perturbations suffered by the optically active (bright) acetylenic CH stretch vibrational state due to vibrational coupling to the nonoptically active (dark) vibrational bath states. (1) The K=0 states are observed to be unperturbed. (2) Approximately 2/3 of the observed K=1–3 transitions are split into 0.02–0.25 cm−1 wide multiplets of two to five lines. These splittings are due to intramolecular coupling of 2ν1 to the near resonant bath states with an average matrix element of 〈V2〉1/2=0.002 cm−1 that appears to grow approximately linearly with K. (3) The K subband origins are observed to be displaced from the positions predicted for a parallel band, symmetric top spectrum.
The first two features suggest that the coupling of the bright state to the bath states is dominated by parallel (z-axis) Coriolis coupling. The third suggests a nonresonant coupling (Coriolis or anharmonic) to a perturber, not directly observed in the spectrum, that itself tunes rapidly with K; the latter being the signature of diagonal z-axis Coriolis interactions affecting the perturber. A natural interpretation of these facts is that the coupling between the bright state and the dark states is mediated by a doorway state that is anharmonically coupled to the bright state and z-axis Coriolis coupled to the dark states. Z-axis Coriolis coupling of the doorway state to the bright state can be ruled out since the ν1 normal mode cannot couple to any of the other normal modes by a parallel Coriolis interaction. Based on the range of measured matrix elements and the distribution of the number of perturbations observed we find that the bath levels that couple to 2ν1 do not exhibit Gaussian orthogonal ensemble type statistics but instead show statistics consistent with a Poisson spectrum, suggesting regular, not chaotic, classical dynamics.
The proton-transfer surface of CH3OHF−
Authors: Wladkowski Brian D. , East Allan L. L. , Mihalick Jennifer E. , Allen Wesley D. , Brauman John I. 
Published: July 2002

Diverse aspects of the potential surface for the proton-transfer reaction CH3OH+F−→CH3O−+HF have been investigated by means of high-level ab initio electronic structure methods based on single-reference wave functions, namely, Mo/ller–Plesset perturbation theory from second through fourth order (MP2–MP4), the configuration interaction and coupled-cluster singles and doubles methods (CISD and CCSD), and CCSD theory augmented by a perturbative correction for connected triple excitations [CCSD(T)]. The one-particle Gaussian basis sets for (C,O,F;H) ranged in quality from [4s2p1d;2s1p] to [14s9p6d4f;9s6p4d], including as many as 482 atomic orbitals for the CH3OHF− system. The ion–molecule complex on the proton-transfer surface is a tight, hydrogen-bonded structure of CH3OH⋅F− character, exhibiting a nearly linear -OHF− framework, an elongated O–H distance of 1.07(1) Å, and a small interfragment separation, r(H–F)=1.32(1) Å. Improved structural data for F−⋅H2O are obtained for calibration purposes. A large fluoride affinity is found for the CH3OHF− adduct, D0=30.4±1 kcal mol−1, and a bonding analysis via the Morokuma decomposition scheme reveals considerable covalent character. The harmonic stretching frequencies within the -OHF− moiety are predicted to be 421 and 2006 cm−1, the latter protonic vibration being downshifted 1857 cm−1 relative to ω1(O–H) of free methanol.
A systematic thermochemical analysis of the reactants and products on the CH3OHF− surface yields a proton-transfer energy of 10.6 kcal mol−1, a gas-phase acidity for methanol of 381.7±1 kcal mol−1, and D0(CH3O–H)=104.1±1 kcal mol−1, facilitating the resolution of previous inconsistencies in associated thermochemical cycles. A minimum-energy path in geometric configuration space is mapped out and parametrized on the basis of constrained structural optimizations for fixed values of an aptly chosen reaction variable. The evaluation of numerous energy points along this path establishes the nonexistence of either a proton-transfer barrier, an inflection region, or a secondary minimum of CH3O−⋅HF type. The mathematical considerations for a classical multipole analysis of reaction path asymptotes are outlined for ion–dipole systems and applied to the CH3OHF− surface with due concern for bifurcations in the exit channel for the proton-transfer process. A global analytic surface for vibrational stretching motion in the -OHF− moiety of the CH3OHF− system is constructed, and a suitable dynamical model is tested which involves an effective, triatomic hydrogen pseudobihalide anion, [-OHF]−. Converged variational eigenstates of [-OHF]− to one-half its dissociation limit are determined using vibrational configuration interaction expansions in terms of self-consistent-field modals. The fundamental stretching frequencies of the CH3OHF− complex predicted by the [-OHF]− model are 504 (+84) and 1456 (−549) cm−1, the corresponding anharmonicities appearing in parentheses.
Dynamics of molecular inversion: An instanton approach
Authors: Smedarchina Zorka , Siebrand Willem , Zgierski Marek Z. , Zerbetto Francesco 
Published: July 2002

To describe tunneling of light atoms, a method is developed that takes account of the multidimensional nature of the process but remains tractable without becoming inaccurate. It combines the instanton formalism with ab initio potentials and force fields and makes effective use of a number of practical approximations suggested by the nature of the calculations. The tunneling potential is constructed from ab initio calculations that are fully optimized at stationary points. All other vibrations are represented by their harmonic force fields. Changes in the harmonic force fields between stationary points are expressed as couplings with the tunneling mode. The transfer rate is calculated for the instanton path, i.e., the path of least resistance, modulated by adjacent paths which define the damping required for nonoscillatory transfer. The multidimensional transfer integrals, involving all modes that change between the initial state and the transition state, are reduced to quasi-one-dimensional integrals by a number of approximation schemes. Modes with frequencies much higher than the tunneling mode are included in the adiabatic potential. Modes with frequencies much lower than the tunneling mode are treated classically. Modes that are linearly coupled to the tunneling mode are handled by separation of the variables followed by analytical integration. These approaches permit the calculation of most transfer rates without the explicit evaluation of the multidimensional instanton path.
They also specify the parts played by the various modes coupled to the tunneling mode. Totally symmetric modes generally promote tunneling by allowing a more favorable trajectory. Hence low-frequency symmetric modes tend to govern the temperature dependence of the transfer. Modes of the same symmetry as the transfer mode will generally contribute to the barrier and thus cause friction, represented by a Franck–Condon factor in the transfer integral. The method is applied to three molecular inversions whose rate constants have been deduced from magnetic resonance measurements. Inversion rate constants for aziridine and the oxiranyl radical together with their relevant deuterium analogs are calculated as a function of temperature and are found to be in a good agreement with the observed rates. For the dioxolanyl radical such agreement is obtained only after the introduction of an anharmonic correction. While inversions are generally low-frequency modes, the method is equally applicable to transfer governed by high-frequency XH stretch vibrations.
Influence of intense equilibrium self-fields on the cyclotron maser instability in high-current gyrotrons
Authors: Uhm Han S. , Davidson Ronald C. 
Published: July 2002

The linearized Vlasov–Maxwell equations are used to investigate the influence of intense equilibrium self-fields on the cyclotron maser instability. A uniform density (n̂b) electron beam propagates parallel to an applied axial magnetic field B0êz with average axial velocity βbc. The particle trajectories are calculated including the influence of the radial self-electric field and the azimuthal self-magnetic field. Moreover, the linearized Vlasov–Maxwell equations are analyzed for body-wave perturbations localized to the beam interior, assuming electromagnetic perturbations about the equilibrium distribution function f0b=(n̂b/2pπ⊥) ×δ(p⊥−γbmV⊥) ×δ(pz−γbmβbc). Near the beam axis (ω2pbr2/c2≪1), it is found that the transverse electron motion is biharmonic, with oscillatory components at the frequencies ω+b and ω−b defined by ω±b =(ωcb/2) ×{1±[1−(2ω2pb/ω2cb) ×(1−β2b)]1/2}. Similarly, the electromagnetic dispersion relation for waves propagating parallel to B0êz exhibits two types of resonance conditions: a high-frequency resonance (HFR) corresponding to ω−kβbc=ω+b, and a low-frequency resonance (LFR) corresponding to ω−kβbc=ω−b.
Both the HFR branch and the LFR branch exhibit instability, with detailed stability properties depending on the value of the self-field parameter s=ω2pb/ω2cb. Moreover, the LFR branch is entirely caused by self-field effects, whereas the HFR branch represents a generalization of the conventional cyclotron maser mode to include self-field effects. The full dispersion relation is analyzed numerically, and the real oscillation frequency ωr=Re ω and growth rate ωi=Im ω are calculated for both types of modes over a wide range of system parameters s, β⊥, βb, and kc/ωcb. Analytic estimates are made of the cyclotron maser growth properties in circumstances where β2⊥γ2z/2 is treated as a small parameter. [Here, γz=(1−β2b)−1/2. ] It is found that the maximum growth rate is given by ωi=(2γ2z)−1 ×[s(2β2⊥γ4z−s)]1/2ωcb, which occurs for wavenumber k=km=γ2zβbωcb/c. As the beam density (s) is increased, the growth rate ωi increases to the maximum value ωmaxi =γ2zβ2⊥ωcb/2 for beam density s=sm=β2⊥γ4z. As s is increased beyond sm, the growth rate ωi decreases to zero for s=s0=2β2⊥γ4z. Similarly, the instability bandwidth Δk =(2γzωcb/c)[γ2z−β−1⊥ ×(s/2)1/2]1/2 approaches zero as s approaches s0.
Ethyl glucuronide—a biological marker for recent alcohol consumption
Authors: Seidl Stephan , Wurst Friedrich M. , Alt Andreas 
Published: July 2002

AbstractEthyl glucuronide (EtG) is a non‐volatile, water‐soluble metabolite of ethanol, with a high storage stability. It can be detected in body fluids, tissues, sweat and hair for an extended time period after the elimination of ethanol from the body. EtG closes the gap between short‐term markers for alcohol consumption such as ethanol or methanol and long‐term markers for alcohol misuse such as GGT, MCV and CDT. Due to its specific time‐frame of detection and its high sensitivity and specificity, EtG is a promising marker for alcohol consumption and for relapse control that enables the therapist to intervene at an early stage of relapsing behaviour. The aim of this review is to give an overview of analytical techniques for the detection of EtG, its clinical use and remaining questions.
Concurrent chronic administration of a CCKB antagonist can decrease tolerance to the ataxic effects of ethanol
Authors: WILSON J. , WOODRUFF G. N. , LITTLE H. J. 
Published: July 2002

AbstractThe effects of chronic administration of a CCKB antagonist, CAM1028, were examined on the development of tolerance to ethanol and the appearance of withdrawal signs. Ethanol was given chronically by liquid diet, and none of the dose schedules of CAM1028 affected the amount of ethanol taken in during the chronic treatment. Brain ethanol concentrations were not altered by the administration of CAM1028.The ataxic effects of ethanol were tested on a rotorod, 3 hours after cessation of the ethanol administration, and the last injections of CAM1028 were given 8 hours before withdrawal from the ethanol treatment. When administered at 0.03, 0.1 or 0.3 mg/kg, CAM1028 decreased the extent of tolerance development. Higher doses, 1 and 3 mg/kg, did not alter the tolerance development. Chronic administration of CAM1028 had a small effect in protecting against the effects of ethanol withdrawal that, in contrast to the effects on the tolerance, was seen only at the highest dose, 10 mg/kg, of CAM1028.
Evidence That Atypical Protein Kinase C-λ and Atypical Protein Kinase C-ζ Participate in Ras-mediated Reorganization of the F-actin Cytoskeleton
Authors: Überall Florian , Hellbert Karina , Kampfer Sonja , Maly Karl , Villunger Andreas , Spitaler Martin , Mwanjewe James , Baier-Bitterlich Gabriele , Baier Gottfried , Grunicke Hans H. 
Published: July 2002

Expression of transforming Ha-Ras L61 in NIH3T3 cells causes profound morphological alterations which include a disassembly of actin stress fibers. The Ras-induced dissolution of actin stress fibers is blocked by the specific PKC inhibitor GF109203X at concentrations which inhibit the activity of the atypical aPKC isotypes λ and ζ, whereas lower concentrations of the inhibitor which block conventional and novel PKC isotypes are ineffective. Coexpression of transforming Ha-Ras L61 with kinase-defective, dominant-negative (DN) mutants of aPKC-λ and aPKC-ζ, as well as antisense constructs encoding RNA-directed against isotype-specific 5′ sequences of the corresponding mRNA, abrogates the Ha-Ras–induced reorganization of the actin cytoskeleton. Expression of a kinase-defective, DN mutant of cPKC-α was unable to counteract Ras with regard to the dissolution of actin stress fibers. Transfection of cells with constructs encoding constitutively active (CA) mutants of atypical aPKC-λ and aPKC-ζ lead to a disassembly of stress fibers independent of oncogenic Ha-Ras. Coexpression of (DN) Rac-1 N17 and addition of the phosphatidylinositol 3′-kinase (PI3K) inhibitors wortmannin and LY294002 are in agreement with a tentative model suggesting that, in the signaling pathway from Ha-Ras to the cytoskeleton aPKC-λ acts upstream of PI3K and Rac-1, whereas aPKC-ζ functions downstream of PI3K and Rac-1.
This model is supported by studies demonstrating that cotransfection with plasmids encoding L61Ras and either aPKC-λ or aPKC-ζ results in a stimulation of the kinase activity of both enzymes. Furthermore, the Ras-mediated activation of PKC-ζ was abrogated by coexpression of DN Rac-1 N17.
What can monotremes tell us about brain evolution?
Authors: Krubitzer Leah 
Published: July 2002

The present review outlines studies of electrophsyiological organization, cortical architecture and thalmocortical and corticocortical connections in monotremes. Results of these studies indicate that the neocortex of monotremes has many features in common with other mammals. In particular, monotremes have at least two, and in some instances three, sensory fields for each modality, as well as regions of bimodal cortex. The internal organization of cortical fields and thalamocortical projection patterns are also similar to those described for other mammals. However, unlike most mammals investigated, the monotreme neocortex has cortical connections between primary sensory fields, such as SI and VI.
The results of this analysis lead us to pose the question of what monotremes can tell us about brain evolution. Monotremes alone can tell us very little about the evolutionary process, or the construction of complex neural networks, as an individual species represents only a single example of what the process is capable of generating. Perhaps a better question is: what can comparative studies tell us about brain evolution? Monotreme brains, when compared with the brains of other animals, can provide some answers to questions about the evolution of the neocortex, the historical precedence of some features over others, and how basic circuits were modified in different lineages. This, in turn, allows us to appreciate how normal circuits function, and to pose very specific questions regarding the development of the neocortex.
Functional control of the binuclear metal site in the metallo‐β‐lactamase‐like fold by subtle amino acid replacements
Authors: Gomes Cláudio M. , Frazão Carlos , Xavier António V. , Legall Jean , Teixeira Miguel 
Published: July 2002

AbstractAt present there are three protein families that share a common structural domain, the αβ/βα fold of class B β‐lactamases: zinc β‐lactamases, glyoxalases II, and A‐type flavoproteins. A detailed inspection of their superimposed structures was undertaken and showed that although these proteins contain binuclear metal sites in spatially equivalent positions, there are some subtle differences within the first ligand sphere that determine a distinct composition of metals. Although zinc β‐lactamases contain either a mono or a di‐zinc center, the catalytically active form of glyoxalase II contains a mixed iron–zinc binuclear center, whereas A‐type flavoproteins contain a di‐iron site. These variations on the type of metal site found within a common fold are correlated with the subtle variations in the nature of the ligating amino acid residues and are discussed in terms of the different reactions catalyzed by each of the protein families. Correlation of these observations with sequence data results in the definition of a sequence motif that comprises the possible binuclear metal site ligands in this broad family. The evolution of the proteins sharing this common fold and factors modulating reactivity are also discussed.
A Population‐Based Study Evaluating Retention in Rheumatology Care Among Patients With Rheumatoid Arthritis
Authors: Barber Claire E. H. , Lacaille Diane , Croxford Ruth , Barnabe Cheryl , Marshall Deborah A. , Abrahamowicz Michal , Xie Hui , Avina‐Zubieta J. Antonio , Esdaile John M. , Hazlewood Glen , Faris Peter , Katz Steven , MacMullan Paul , Mosher Dianne , Widdifield Jessica 
Published: May 2022

ObjectiveThe study objective was to assess adherence to system‐level performance measures measuring retention in rheumatology care and disease modifying anti‐rheumatic drug (DMARD) treatment in rheumatoid arthritis (RA).MethodsWe used a validated health administrative data case definition to identify individuals with RA in Ontario, Canada, between 2002 and 2014 who had at least 5 years of potential follow‐up prior to 2019. During the first 5 years following diagnosis, we assessed whether patients were seen by a rheumatologist yearly and the proportion dispensed a DMARD yearly (in those aged ≥66 for whom medication data were available). Multivariable logistic regression analyses were used to estimate the odds of remaining under rheumatologist care.ResultsThe cohort included 50,883 patients with RA (26.1% aged 66 years and older). Over half (57.7%) saw a rheumatologist yearly in all 5 years of follow‐up. Sharp declines in the percentage of patients with an annual visit were observed in each subsequent year after diagnosis, although a linear trend to improved retention in rheumatology care was seen over the study period (P < 0.0001). For individuals aged 66 years or older (n = 13,293), 82.1% under rheumatologist care during all 5 years after diagnosis were dispensed a DMARD annually compared with 31.0% of those not retained under rheumatology care. Older age, male sex, lower socioeconomic status, higher comorbidity score, and having an older rheumatologist decreased the odds of remaining under rheumatology care.ConclusionSystem‐level improvement initiatives should focus on maintaining ongoing access to rheumatology specialty care. Further investigation into causes of loss to rheumatology follow‐up is needed.
Phase Separation: “The Master Key” to Deciphering the Physiological and Pathological Functions of Cells
Authors: Wei Chuzhong , Li Mingdong , Li Xinming , Lyu Jianxin , Zhu Xiao 
Published: May 2022

AbstractPhase separation is a hot research field at present. It involves almost all aspects of cells and plays a significant role in cells, promising to be “a master key” in unlocking the mysteries of nature. In this review, the factors that affect phase separation are introduced, such as own component, electrostatic interaction, and chemical modification. Furthermore, the physiological roles of phase separation in cells, including molecules transport channel, gene expression and regulation, cellular division and differentiation, stress response, proteins refolding and degradation, cell connections, construction of skin barrier, and cell signals transmission, are highlighted. However, the disorder of phase separation leads to pathological condensates, which are associated with neurodegenerative diseases, tumors, and severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2). This relationship is considered the potential target for developing corresponded drugs and therapy. Some drugs targeting phase separation have improved meaningful, such as tankyrase, lipoamide, oligonucleotides, elvitagravir, nilotinib, CVL218, PJ34. All in all, mystery phase separation provides a new viewpoint for researchers to explore cells, and is expected to solve many unknown phenomena in nature.