RESUMO
BACKGROUND: Pre-diagnostic stages of psychotic illnesses, including 'clinical high risk' (CHR), are marked by sleep disturbances. These sleep disturbances appear to represent a key aspect in the etiology and maintenance of psychotic disorders. We aimed to examine the relationship between self-reported sleep dysfunction and attenuated psychotic symptoms (APS) on a day-to-day basis. METHODS: Seventy-six CHR young people completed the Experience Sampling Methodology (ESM) component of the European Union Gene-Environment Interaction Study, collected through PsyMate® devices, prompting sleep and symptom questionnaires 10 times daily for 6 days. Bayesian multilevel mixed linear regression analyses were performed on time-variant ESM data using the brms package in R. We investigated the day-to-day associations between sleep and psychotic experiences bidirectionally on an item level. Sleep items included sleep onset latency, fragmentation, and quality. Psychosis items assessed a range of perceptual, cognitive, and bizarre thought content common in the CHR population. RESULTS: Two of the seven psychosis variables were unidirectionally predicted by previous night's number of awakenings: every unit increase in number of nightly awakenings predicted a 0.27 and 0.28 unit increase in feeling unreal or paranoid the next day, respectively. No other sleep variables credibly predicted next-day psychotic symptoms or vice-versa. CONCLUSION: In this study, the relationship between sleep disturbance and APS appears specific to the item in question. However, some APS, including perceptual disturbances, had low levels of endorsement amongst this sample. Nonetheless, these results provide evidence for a unidirectional relationship between sleep and some APS in this population.
Assuntos
Transtornos Psicóticos , Transtornos do Sono-Vigília , Humanos , Transtornos Psicóticos/fisiopatologia , Feminino , Masculino , Adolescente , Adulto Jovem , Transtornos do Sono-Vigília/fisiopatologia , Transtornos do Sono-Vigília/epidemiologia , Adulto , Teorema de Bayes , Avaliação Momentânea Ecológica , Autorrelato , Interação Gene-Ambiente , Inquéritos e Questionários , Sintomas ProdrômicosRESUMO
Adverse surgical events cause negative patient health outcomes and harm that can often overshadow the safe and effective patient care provided daily by nurses as members of interprofessional healthcare teams. Near misses occur far more frequently than adverse events and are less visible to nurse leaders because patient harm is avoided due to chance, prevention, or mitigation. However, near misses have comparable root causes to adverse events and exhibit the same underlying patterns of failure. Reviewing near misses provides nurses with learning opportunities to identify patient care weaknesses and build appropriate solutions to enhance care. As the operating room is one of the most complex work settings in healthcare, identifying potential weaknesses or sources for errors is vital to reduce healthcare-associated risks for patients and staff. The purpose of this manuscript is to educate, inform, and stimulate critical thinking by discussing perioperative near miss case studies and the underlying factors that lead to errors. Our authors discuss 15 near miss case studies occurring across the perioperative patient experience of care and discuss barriers to near miss reporting. Nurse leaders can use our case studies to stimulate discussion among perioperative and perianesthesia nurses in their hospitals to inform comprehensive risk reduction programs.
Assuntos
Near Miss , Gestão de Riscos , Humanos , Segurança do Paciente , Salas Cirúrgicas , Acidentes , Erros Médicos/prevenção & controleRESUMO
Probability distortion-the tendency to underweight larger probabilities and overweight smaller ones-is a robust empirical phenomenon and an important driver of suboptimal choices. We reveal a novel contextual effect on probability distortion that depends on the composition of the choice set. Probability distortion was larger in a magnitude-diverse choice set (in which participants encountered more unique magnitudes than probabilities) but declined, resulting in more veridical weighting, in a probability-diverse choice set (more unique probabilities than magnitudes). This effect was consistent in two, large, independent datasets (N = 481, N = 100) and held for a subset of lotteries that were identical in the two contexts. It also developed gradually as a function of exposure to the choice set, was independent of attentional biases to probability versus magnitude information, and was specific to probability weighting, leaving risk attitudes unaffected. The results highlight the importance of context when processing probabilistic information.
Assuntos
Viés de Atenção , Humanos , Probabilidade , Atitude , Comportamento de Escolha , Tomada de Decisões , Assunção de RiscosRESUMO
We propose a Markovian quantum model for the time dependence of the pressure-induced decoherence of rotational wave packets of gas-phase molecules beyond the secular approximation. It is based on a collisional relaxation matrix constructed using the energy-corrected sudden approximation, which improves the previously proposed infinite order sudden one by taking the molecule rotation during collisions into account. The model is tested by comparisons with time-domain measurements of the pressure-induced decays of molecular-axis alignment features (revivals and echoes) for HCl and CO2 gases, pure and diluted in He. For the Markovian systems HCl-He and CO2-He, the comparisons between computed and measured data demonstrate the robustness of our approach, even when the secular approximation largely breaks down. In contrast, significant differences are obtained in the cases of pure HCl and CO2, for which the model underestimates the decay rate of the alignment at short times. This result is attributed to the non-Markovianity of HCl-HCl and CO2-CO2 interactions and the important contribution of those collisions that are ongoing at the time when the system is excited by the aligning laser pulse.
RESUMO
The target asymmetry T, recoil asymmetry P, and beam-target double polarization observable H were determined in exclusive π0 and η photoproduction off quasi-free protons and, for the first time, off quasi-free neutrons. The experiment was performed at the electron stretcher accelerator ELSA in Bonn, Germany, with the Crystal Barrel/TAPS detector setup, using a linearly polarized photon beam and a transversely polarized deuterated butanol target. Effects from the Fermi motion of the nucleons within deuterium were removed by a full kinematic reconstruction of the final state invariant mass. A comparison of the data obtained on the proton and on the neutron provides new insight into the isospin structure of the electromagnetic excitation of the nucleon. Earlier measurements of polarization observables in the γpâπ0p and γpâηp reactions are confirmed. The data obtained on the neutron are of particular relevance for clarifying the origin of the narrow structure in the ηn system at W=1.68GeV. A comparison with recent partial wave analyses favors the interpretation of this structure as arising from interference of the S11(1535) and S11(1650) resonances within the S11-partial wave.
RESUMO
GeSn alloys are the most promising direct band gap semiconductors to demonstrate full CMOS-compatible laser integration with a manufacturing from Group-IV materials. Here, we show that room temperature lasing, up to 300 K, can be obtained with GeSn. This is achieved in microdisk resonators fabricated on a GeSn-On-Insulator platform by combining strain engineering with a thick layer of high Sn content GeSn.
RESUMO
Vertical nanostructure technologies are becoming more important for the down scaling of nanoelectronic devices such as logic transistors or memories. Such devices require dense vertical nanostructured channel arrays (VNCA) that can be fabricated through a top-down approach based on group IV materials. We present progresses on the top-down fabrication of highly anisotropic and ultra-dense Si1-xGex(x= 0, 0.2, 0.5) VNCAs. Dense nanowire and nanosheet patterns were optimized through high resolution lithography and transferred onto Si1-xGexsubstrates by anisotropic reactive ion etching with a fluorine chemistry. The right gas mixtures for a given Ge content resulted in perfectly vertical and dense arrays. Finally we fabricated oxide shell/SiGe core heterostructures by dry- and wet-thermal oxidation and evaluated their applicability for nanostructure size engineering, as already established for silicon nanowires. The impact of the nanostructured shape (wire or sheet), size and Ge content on the oxide growth were investigated and analysed in detail through transmission electron microscopy.
RESUMO
Viscoelastic haemostatic assays provide rapid testing at the bed-side that identify all phases of haemostasis, from initial fibrin formation to clot lysis. In obstetric patients, altered haemostasis is common as pregnancy is associated with coagulation changes that may contribute to bleeding events such as postpartum haemorrhage, as well as thrombosis events. In this narrative review, we examine the potential clinical utility of viscoelastic haemostatic assays in postpartum haemorrhage and consider the current recommendations for their use in obstetric patients. We discuss the clinical benefits associated with the use of viscoelastic haemostatic assays due to the provision of (near) real-time readouts with a short turnaround, coupled with the identification of coagulation defects such as hypofibrinogenaemia. The use of viscoelastic haemostatic assay-guided algorithms may be beneficial to diagnose coagulopathy, predict postpartum haemorrhage, reduce transfusion requirements and monitor fibrinolysis in women with obstetric haemorrhage. Further studies are required to assess whether viscoelastic haemostatic assay-guided treatment improves clinical outcomes, and to confirm the utility of prepartum viscoelastic haemostatic assay measurements for identifying patients at risk of postpartum haemorrhage.
Assuntos
Transtornos da Coagulação Sanguínea , Hemostáticos , Hemorragia Pós-Parto , Transtornos da Coagulação Sanguínea/terapia , Feminino , Hemostasia , Hemostáticos/uso terapêutico , Humanos , Sistemas Automatizados de Assistência Junto ao Leito , Hemorragia Pós-Parto/tratamento farmacológico , Hemorragia Pós-Parto/terapia , Gravidez , TromboelastografiaRESUMO
BACKGROUND: In 2004, we started an intergroup randomized trial of adjuvant imatinib versus no further therapy after R0-R1 surgery in localized, high/intermediate-risk gastrointestinal stromal tumors (GIST) patients. Interim analysis results were published in 2015 upon recommendation from an independent data review committee. We report the final outcome of the study. PATIENTS AND METHODS: This was a randomized, open-label, multicenter phase III trial carried out at 112 hospitals in 12 countries. Patients were randomized to 2 years of imatinib, 400 mg daily, or no further therapy after surgery. The primary endpoint was imatinib failure-free survival (IFFS), while relapse-free survival (RFS), relapse-free interval (RFI), overall survival (OS) and toxicity were secondary endpoints. Adjusting for the interim analyses, results on IFFS were assessed on a 4.3% significance level; for the other endpoints, 5% was used. RESULTS: Nine hundred and eight patients were randomized between January 2005 and October 2008: 454 to imatinib and 454 to observation; 835 patients were eligible. With a median follow-up of 9.1 years, 5 (10)-year IFFS was 87% (75%) in the imatinib arm versus 83% (74%) in the control arm [hazard ratio (HR) = 0.87, 95.7% confidence interval (CI) (0.65; 1.15), P = 0.31]; RFS was 70% versus 63% at 5 years and 63% versus 61% at 10 years, [HR = 0.71, 95% CI (0.57; 0.89), P = 0.002]; OS was 93% versus 92% at 5 years and 80% versus 78% at 10 years [HR = 0.88, 95% CI (0.65; 1.21), P = 0.43]. Among 526 patients with high-risk GIST by local pathology, 10-year IFFS and RFS were 69% versus 61%, and 48% versus 43%, respectively. CONCLUSIONS: With 9.1 years of follow-up, a trend toward better long-term IFFS in imatinib-treated patients was observed in the high-risk subgroup. Although the difference was not statistically significant and the surrogacy value of such an endpoint is not validated, this may be seen as supporting the results reported by the Scandinavian/German trial, showing a sustained small but significant long-term OS benefit in high-risk GIST patients treated with 3 years of adjuvant imatinib.
Assuntos
Antineoplásicos , Neoplasias Gastrointestinais , Tumores do Estroma Gastrointestinal , Sarcoma , Antineoplásicos/uso terapêutico , Quimioterapia Adjuvante , Neoplasias Gastrointestinais/tratamento farmacológico , Tumores do Estroma Gastrointestinal/tratamento farmacológico , Humanos , Mesilato de Imatinib/uso terapêutico , Itália , Recidiva Local de Neoplasia/tratamento farmacológico , Sarcoma/tratamento farmacológicoRESUMO
A measurement of the double-polarization observable E for the reaction γ p â π 0 p is reported. The data were taken with the CBELSA/TAPS experiment at the ELSA facility in Bonn using the Bonn frozen-spin butanol (C 4 H 9 OH) target, which provided longitudinally-polarized protons. Circularly-polarized photons were produced via bremsstrahlung of longitudinally-polarized electrons. The data cover the photon energy range from E γ = 600 to 2310 MeV and nearly the complete angular range. The results are compared to and have been included in recent partial wave analyses.
RESUMO
Data on the beam asymmetry Σ in the photoproduction of η mesons off protons are reported for tagged photon energies from 1130 to 1790 MeV (mass range from W=1748 MeV to W=2045 MeV). The data cover the full solid angle that allows for a precise moment analysis. For the first time, a strong cusp effect in a polarization observable has been observed that is an effect of a branch-point singularity at the pη^{'} threshold [E_{γ}=1447 MeV (W=1896 MeV)]. The latest BnGa partial wave analysis includes the new beam asymmetry data and yields a strong indication for the N(1895)1/2^{-} nucleon resonance, demonstrating the importance of including all singularities for a correct determination of partial waves and resonance parameters.
RESUMO
BACKGROUND: The integration of various domains or levels of analysis (clinical, neurobiological, genetic, etc.) has been a challenge in schizophrenia research. A promising approach is to use the core phenomenological features of the disorder as an organising principle for other levels of analysis. Minimal self-disturbance (fragility in implicit first-person perspective, presence and agency) is emerging as a strong candidate to play this role. This approach was adopted in a previously described theoretical neurophenomenological model that proposed that source monitoring deficits and aberrant salience may be neurocognitive/neurobiological processes that correlate with minimal self-disturbance on the phenomenological level, together playing an aetiological role in the onset of schizophrenia spectrum disorders. The current paper presents full cross-sectional data from the first empirical test of this model. METHODS: Fifty ultra-high risk for psychosis patients, 39 first episode psychosis patients and 34 healthy controls were assessed with a variety of clinical measures, including the Examination of Anomalous Self-Experience (EASE), and neurocognitive and neurophysiological (EEG) measures of source monitoring deficits and aberrant salience. RESULTS: Linear regression indicated that source monitoring (composite score across neurocognitive and neurophysiological measures), with study group as an interaction term, explained 39.8% of the variance in EASE scores (R2â¯=â¯0.41, F(3,85)â¯=â¯14.78, pâ¯<â¯0.001), whereas aberrant salience (composite score) explained only 6% of the variance in EASE scores (R2â¯=â¯0.06, F(3,85)â¯=â¯1.44, pâ¯=â¯0.93). Aberrant salience measures were more strongly related to general psychopathology measures, particularly to positive psychotic symptoms, than to EASE scores. DISCUSSION: A neurophenomenological model of minimal self-disturbance in schizophrenia spectrum disorders may need to be expanded from source monitoring deficits to encompass other relevant constructs such as temporal processing, intermodal/multisensory integration, and hierarchical predictive processing. The cross-sectional data reported here will be expanded with longitudinal analysis in subsequent reports. These data and other related recent research show an emerging picture of neuro-features of core phenomenological aspects of schizophrenia spectrum disorders beyond surface-level psychotic symptoms.
Assuntos
Conscientização/fisiologia , Potenciais Evocados/fisiologia , Atividade Motora/fisiologia , Transtornos Psicóticos/fisiopatologia , Reconhecimento Psicológico/fisiologia , Esquizofrenia/fisiopatologia , Adolescente , Adulto , Estudos Transversais , Suscetibilidade a Doenças , Eletroencefalografia , Feminino , Humanos , Imaginação/fisiologia , Masculino , Modelos Biológicos , Sintomas Prodrômicos , Autoimagem , Adulto JovemRESUMO
Atrial fibrillation (AF) is the most frequent persistent cardiac arrhythmia and is associated with an increased mortality. Therefore, an effective differential treatment of patients is mandatory. After a risk stratification oral anticoagulation (OAC) should be initiated depending on the individual stroke risk of each patient. Alternatively, in the presence of contraindications for OAC and an increased risk for bleeding and/or stroke, the implantation of a left atrial appendage closure device can be considered. Symptomatic patients should undergo a rhythm control strategy if possible. Based on the risk-benefit considerations, catheter ablation (CA) of AF plays an increasingly important role in establishing long-term medicinal rhythm control. A pulmonary vein isolation can lead to freedom from AF for 1 year in 70-80% of patients with paroxysmal AF (and approximately 50% in persistent AF). So far, a survival advantage of CA could only be shown in patients with heart failure, so that in most cases this is only a symptomatic treatment for improvement in the quality of life.
Assuntos
Apêndice Atrial , Fibrilação Atrial , Ablação por Cateter , Veias Pulmonares , Apêndice Atrial/cirurgia , Fibrilação Atrial/tratamento farmacológico , Fibrilação Atrial/cirurgia , Humanos , Qualidade de Vida , Resultado do TratamentoRESUMO
We show that recently discovered rotational echoes of molecules provide an efficient tool for studying collisional molecular dynamics in high-pressure gases. Our study demonstrates that rotational echoes enable the observation of extremely fast collisional dissipation, at timescales of the order of a few picoseconds, and possibly shorter. The decay of the rotational alignment echoes in CO_{2} gas and CO_{2}-He mixture up to 50 bar was studied experimentally, delivering collision rates that are in good agreement with the theoretical expectations. The suggested measurement protocol may be used in other high-density media, and potentially in liquids.
RESUMO
Single-nucleotide polymorphisms (SNPs) in CACNA1C, the α1C subunit of the voltage-gated L-type calcium channel Cav1.2, rank among the most consistent and replicable genetics findings in psychiatry and have been associated with schizophrenia, bipolar disorder and major depression. However, genetic variants of complex diseases often only confer a marginal increase in disease risk, which is additionally influenced by the environment. Here we show that embryonic deletion of Cacna1c in forebrain glutamatergic neurons promotes the manifestation of endophenotypes related to psychiatric disorders including cognitive decline, impaired synaptic plasticity, reduced sociability, hyperactivity and increased anxiety. Additional analyses revealed that depletion of Cacna1c during embryonic development also increases the susceptibility to chronic stress, which suggest that Cav1.2 interacts with the environment to shape disease vulnerability. Remarkably, this was not observed when Cacna1c was deleted in glutamatergic neurons during adulthood, where the later deletion even improved cognitive flexibility, strengthened synaptic plasticity and induced stress resilience. In a parallel gene × environment design in humans, we additionally demonstrate that SNPs in CACNA1C significantly interact with adverse life events to alter the risk to develop symptoms of psychiatric disorders. Overall, our results further validate Cacna1c as a cross-disorder risk gene in mice and humans, and additionally suggest a differential role for Cav1.2 during development and adulthood in shaping cognition, sociability, emotional behavior and stress susceptibility. This may prompt the consideration for pharmacological manipulation of Cav1.2 in neuropsychiatric disorders with developmental and/or stress-related origins.
Assuntos
Canais de Cálcio Tipo L/genética , Canais de Cálcio Tipo L/fisiologia , Transtornos Mentais/genética , Adulto , Negro ou Afro-Americano , Animais , Transtorno Bipolar/genética , Canais de Cálcio/genética , Transtorno Depressivo Maior/genética , Modelos Animais de Doenças , Feminino , Predisposição Genética para Doença/genética , Variação Genética/genética , Humanos , Masculino , Camundongos/embriologia , Camundongos Transgênicos/genética , Neurônios/metabolismo , Polimorfismo de Nucleotídeo Único/genética , Esquizofrenia/genéticaRESUMO
BACKGROUND: Risk factors for primary non-melanoma skin cancer (NMSC) in organ transplant recipients (OTR) have been well described. Data for subsequent NMSC and dynamics in their occurrence in OTR are limited. OBJECTIVE: To study long-term risks of primary and subsequent NMSC and associated risk factors in OTR. METHODS: A retrospective single-centre cohort study analysing medical records from a dermato-oncological specialty clinic. RESULTS: Of 464 OTR 110 (23.7%) developed at least one, 73 (15.7%) two and 51 (11%) three NMSC during a median follow-up of 9.6 years. Cumulative incidences at 5, 10 and 15 years were 14.7%, 23.5% and 34.5% for the first and 75.8%, 86.5% and 93.3% for the second. Median time-to-diagnosis declined from 22 years (95% CI 19-25) to 2 years (1-3) and about 1 year (0-2) for the first, second and third NMSC. Risk for subsequent NMSC only partially related to risk factors for the primary NMSC. Histologic type of the first NMSC predicted subtype and time-to-diagnosis of the subsequent NMSC. CONCLUSIONS: A first post-transplant NMSC, particularly a SCC, confers a high risk for subsequent NMSC arising with accelerated dynamics. Risk-adapted dermato-oncologic surveillance is advisable for all OTR.
Assuntos
Carcinoma Basocelular/epidemiologia , Carcinoma de Células Escamosas/epidemiologia , Recidiva Local de Neoplasia/epidemiologia , Segunda Neoplasia Primária/epidemiologia , Transplante de Órgãos , Neoplasias Cutâneas/epidemiologia , Adulto , Carcinoma Basocelular/patologia , Carcinoma de Células Escamosas/patologia , Feminino , Alemanha/epidemiologia , Humanos , Incidência , Masculino , Pessoa de Meia-Idade , Recidiva Local de Neoplasia/patologia , Segunda Neoplasia Primária/patologia , Período Pós-Operatório , Estudos Retrospectivos , Fatores de Risco , Neoplasias Cutâneas/patologia , Fatores de Tempo , Adulto JovemRESUMO
Anxiety disorders constitute a major disease and social burden worldwide; however, many questions concerning the underlying molecular mechanisms still remain open. Besides the involvement of the major excitatory (glutamate) and inhibitory (gamma aminobutyric acid (GABA)) neurotransmitter circuits in anxiety disorders, the stress system has been directly implicated in the pathophysiology of these complex mental illnesses. The glucocorticoid receptor (GR) is the major receptor for the stress hormone cortisol (corticosterone in rodents) and is widely expressed in excitatory and inhibitory neurons, as well as in glial cells. However, currently it is unknown which of these cell populations mediate GR actions that eventually regulate fear- and anxiety-related behaviors. In order to address this question, we generated mice lacking the receptor specifically in forebrain glutamatergic or GABAergic neurons by breeding GRflox/flox mice to Nex-Cre or Dlx5/6-Cre mice, respectively. GR deletion specifically in glutamatergic, but not in GABAergic, neurons induced hypothalamic-pituitary-adrenal axis hyperactivity and reduced fear- and anxiety-related behavior. This was paralleled by reduced GR-dependent electrophysiological responses in the basolateral amygdala (BLA). Importantly, viral-mediated GR deletion additionally showed that fear expression, but not anxiety, is regulated by GRs in glutamatergic neurons of the BLA. This suggests that pathological anxiety likely results from altered GR signaling in glutamatergic circuits of several forebrain regions, while modulation of fear-related behavior can largely be ascribed to GR signaling in glutamatergic neurons of the BLA. Collectively, our results reveal a major contribution of GRs in the brain's key excitatory, but not inhibitory, neurotransmitter system in the regulation of fear and anxiety behaviors, which is crucial to our understanding of the molecular mechanisms underlying anxiety disorders.
Assuntos
Transtornos de Ansiedade/fisiopatologia , Receptores de Glucocorticoides/metabolismo , Receptores de Glutamato/metabolismo , Tonsila do Cerebelo/metabolismo , Animais , Ansiedade/fisiopatologia , Complexo Nuclear Basolateral da Amígdala/metabolismo , Corticosterona/metabolismo , Fármacos Atuantes sobre Aminoácidos Excitatórios/metabolismo , Medo/fisiologia , GABAérgicos/metabolismo , Neurônios GABAérgicos/metabolismo , Ácido Glutâmico/metabolismo , Sistema Hipotálamo-Hipofisário/metabolismo , Camundongos , Camundongos Knockout , Neurônios/metabolismo , Sistema Hipófise-Suprarrenal/metabolismo , Prosencéfalo/metabolismo , Transmissão Sináptica/fisiologia , Ácido gama-Aminobutírico/metabolismoRESUMO
In this paper, SiGe nano-heteroepitaxy on Si and SiGe nano-pillars was investigated in a 300 mm industrial reduced pressure-chemical vapour deposition tool. An integration scheme based on diblock copolymer patterning was used to fabricate nanometre-sized templates for the epitaxy of Si and SiGe nano-pillars. Results showed highly selective and uniform processes for the epitaxial growth of Si and SiGe nano-pillars. 200 nm thick SiGe layers were grown on Si and SiGe nano-pillars and characterised by atomic force microscopy, x-ray diffraction and transmission electron microscopy. Smooth SiGe surfaces and full strain relaxation were obtained in the 650 °C-700 °C range for 2D SiGe layers grown either on Si or SiGe nano-pillars.
RESUMO
We present the first quantum mechanical model of the collisional dissipation of the alignment of a gas of symmetric-top molecules (ethane) impulsively induced by a linearly polarized non-resonant laser field. The approach is based on use of the Bloch model and of the Markov and secular approximations in which the effects of collisions are taken into account through the state-to-state rates associated with exchanges among the various rotational states. These rates are constructed using the Energy Corrected Sudden (ECS) approximation with (a few) input parameters obtained independently from fits of the pressure-broadening coefficients of ethane absorption lines. Based on knowledge of the laser pulse characteristics and on these rates, the time-dependent equation driving the evolution of the density matrix during and after the laser pulse is solved and the time dependence of the so-called "alignment factor" is computed. Comparisons with measurements, free of any adjusted parameter, show that the proposed approach leads to good agreement with measurements. The analysis of the ECS state-to-state collisional rates demonstrates that, as in the case of linear molecules, collision-induced changes of the rotational angular momentum orientation are slower than those of its magnitude. This explains why the collisional decay of the permanent component of the alignment is significantly slower than that of the amplitudes of the transient revivals in both experimental and computed results. It is also shown that, since intermolecular forces within C2H6 colliding pairs weakly depend on rotations of the molecules around their C-C bond, the dissipation mechanism of the alignment in pure ethane is close to that involved in linear molecules.
RESUMO
We present the first theoretical study of collisional dissipation of the alignment of a symmetric-top molecule (ethane gas) impulsively induced by a linearly polarized non-resonant laser field. For this, Classical Molecular Dynamics Simulations (CMDSs) are carried out for an ensemble of C2H6 molecules based on knowledge of the laser-pulse characteristics and on an input intermolecular potential. These provide, for a given gas pressure and initial temperature, the orientations of all molecules at all times from which the alignment factor is directly obtained. Comparisons with measurements show that these CMDSs well predict the permanent alignment induced by the laser pulse and its decay with time but, as expected, fail in generating alignment revivals. However, it is shown that introducing a simple requantization procedure in the CMDS "creates" these revivals and that their predicted dissipation decay agrees very well with measured values. The calculations also confirm that, as for linear molecules, the permanent alignment of ethane decays more slowly than the transient revivals. The influence of the intermolecular potential is studied as well as that of the degree of freedom associated with the molecular rotation around the symmetry axis. This reveals that ethane practically behaves as a linear molecule because the intermolecular potential is only weakly sensitive to rotation around the C-C axis.