360 research outputs found

    The Exact Wavefunction Factorization of a Vibronic Coupling System

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    We investigate the exact wavefunction as a single product of electronic and nuclear wavefunction for a model conical intersection system. Exact factorized spiky potentials and nodeless nuclear wavefunctions are found. The exact factorized potential preserves the symmetry breaking effect when the coupling mode is present. Additionally the nodeless wavefunctions are found to be closely related to the adiabatic nuclear eigenfunctions. This phenomenon holds even for the regime where the non-adiabatic coupling is relevant, and sheds light on the relation between the exact wavefunction factorization and the adiabatic approximation

    Nuclear Dynamics in Electronic Decay Processes followed by Fragmentation

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    The impact of the nuclear dynamics during an electronic decay process followed by fragmentation in a diatomic system is investigated for three different examples, by using a time-dependent approach. The first example is the prediction of the interatomic Coulombic decay (ICD) process in NeAr, following the Ne 1s Auger decay. It is a two-step (cascade) decay process where the first step is a fast Auger decay and the second step is the ICD of interest. A full cascade calculation has been performed to provide the (time-resolved) Auger electron and (time-resolved) ICD electron spectra. Our results show that the line width of the Auger electron spectrum contains also the information on the total ICD width at the equilibrium internuclear distance of NeAr. In addition, simulations show that the nuclear motion during the first Auger step has no impact on the following ICD process. This ICD process has been verified by experiment, and if a simple modification of the ab initio ICD transition rate is adopted, our simulated ICD spectrum agrees well with the experimental result. For an electronic decay process followed by fragmentation, the energy spectrum of the emitted electron and the kinetic energy release (KER) spectrum of the ionic fragments are usually considered to be mirror images of each other. This is termed "mirror image principle" and is often applied in experiments. It is usually valid for the ICD electron spectrum and its corresponding KER spectrum. However, the principle is merely an empirical rule and can break down even in a diatomic system. The molecular Auger process in CO is chosen as the second example, as it exhibits such a break down of the mirror image principle. Calculated KER and electron spectra for this process also agree well with experiment. The resonant Auger process of HCl is chosen as the last example to demonstrate that the interaction between a molecule and an intense laser pulse (as are available today in free electron lasers) can lead to a strong light-induced non-adiabatic effect. It is a general effect that can be found in molecules interacting with an intense laser pulse, which gives rise to strong molecular overall rotation. Besides the above applications, a new elegant and numerically efficient formulation for evaluating the (time-resolved) KER spectrum in an electronic decay process followed by fragmentation is derived in this work. The KER spectrum now has a simple physical interpretation: it is the accumulated (over time) generalized Franck-Condon factor between the nuclear wave packet on the intermediate decaying state and the discrete continuum eigenfunctions of the dissociative final state. This new representation allows one to analyze the KER and the electron spectra, and it provides the conditions for the mirror image principle to hold

    Accuracy of Potfit-based potential representations and its impact on the performance of (ML-)MCTDH

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    Quantum molecular dynamics simulations with MCTDH or ML-MCTDH perform best if the potential energy surface (PES) has a sum-of-products (SOP) or multi-layer operator (MLOp) structure. Here we investigate four different POTFIT-based methods for representing a general PES as such a structure, among them the novel random-sampling multi-layer Potfit (RS-MLPF). We study how the format and accuracy of the PES representation influences the runtime of a benchmark (ML-)MCTDH calculation, namely the computation of the ground state of the H3O2{\text{H}_3\text{O}_2}^- ion. Our results show that compared to the SOP format, the MLOp format leads to a much more favorable scaling of the (ML-)MCTDH runtime with the PES accuracy. At reasonably high PES accuracy, ML-MCTDH calculations thus become up to 20 times faster, and taken to the extreme, the RS-MLPF method yields extremely accurate PES representations (global root-mean-square error of 0.1cm1\sim 0.1\,\text{cm}^{-1}) which still lead to only moderate computational demands for ML-MCTDH.Comment: (C) 2017. This manuscript version is made available under the CC-BY-NC-ND 4.0 license. http://creativecommons.org/licenses/by-nc-nd/4.0

    Resonant Auger decay of the core-excited C^\astO molecule in intense X-ray laser fields

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    The dynamics of the resonant Auger (RA) process of the core-excited C^\astO(1s1π,vr=0^{-1}\pi^\ast,v_r=0) molecule in an intense X-ray laser field is studied theoretically. The theoretical approach includes the analogue of the conical intersections of the complex potential energy surfaces of the ground and `dressed' resonant states due to intense X-ray pulses, taking into account the decay of the resonance and the direct photoionization of the ground state, both populating the same final ionic states coherently, as well as the direct photoionization of the resonance state itself. The light-induced non-adiabatic effect of the analogue of the conical intersections of the resulting complex potential energy surfaces gives rise to strong coupling between the electronic, vibrational and rotational degrees of freedom of the diatomic CO molecule. The interplay of the direct photoionization of the ground state and of the decay of the resonance increases dramatically with the field intensity. The coherent population of a final ionic state via both the direct photoionization and the resonant Auger decay channels induces strong interference effects with distinct patterns in the RA electron spectra. The individual impact of these physical processes on the total electron yield and on the CO+(A2Π)^+(A^2\Pi) electron spectrum are demonstrated.Comment: 13 figs, 1 tabe

    Asymmetric ephaptic inhibition between compartmentalized olfactory receptor neurons.

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    In the Drosophila antenna, different subtypes of olfactory receptor neurons (ORNs) housed in the same sensory hair (sensillum) can inhibit each other non-synaptically. However, the mechanisms underlying this underexplored form of lateral inhibition remain unclear. Here we use recordings from pairs of sensilla impaled by the same tungsten electrode to demonstrate that direct electrical ("ephaptic") interactions mediate lateral inhibition between ORNs. Intriguingly, within individual sensilla, we find that ephaptic lateral inhibition is asymmetric such that one ORN exerts greater influence onto its neighbor. Serial block-face scanning electron microscopy of genetically identified ORNs and circuit modeling indicate that asymmetric lateral inhibition reflects a surprisingly simple mechanism: the physically larger ORN in a pair corresponds to the dominant neuron in ephaptic interactions. Thus, morphometric differences between compartmentalized ORNs account for highly specialized inhibitory interactions that govern information processing at the earliest stages of olfactory coding

    Toward Optimal Resource Allocation of Virtualized Network Functions for Hierarchical Datacenters

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    Telecommunications service providers (TSPs) previously provided network functions to end users with dedicated hardware, but they are resorting to virtualized infrastructure for reducing costs and increasing flexibility in resource allocation. A representative case is the Central Office Re-architected as Datacenter (CORD) project from AT&T, which aims to deploy virtualized network functions (VNFs) to over 4000 central offices (COs) across the U.S. However, there is a wide spectrum of options for deploying VNFs over the COs, varying from highly distributed to highly centralized manners. The former benefits end users with short response time but has its inherent limitation on utilizing geographically dispersed resources, while the latter allows resources to be better utilized at a cost of longer response time. In this work, we model the TSP's virtualized infrastructure as hierarchical datacenters, namely hierarchical CORD, and provide a resource allocation solution to strike the optimal balance between the two extreme options. Our evaluations reveal that in general, the 3-tier architecture incurs the least cost in case of deploying VNFs under moderate or loose delay constraints. Furthermore, the margin of improvement on the resource allocation cost increases inversely with the overall system utilization rate. Our results also suggest that as heavy request load overwhelms the network infrastructure, the relevant VNFs shall be migrated to lower-tier edge datacenters or to some nearby datacenters with superior network capacity. The evaluations also demonstrate that the proposed model allows highly adaptive VNF deployment in the hierarchical architecture under various conditions.This work was supported in part by H2020 Collaborative Europe/Taiwan Research Project 5G-CORAL under Grant 761586, and in part by the Ministry of Science and Technology, Taiwan, under Grant MOST-106-2218-E-009-018 and Grant MOST-106-2221-E-194-021-MY3

    New primers for methylation-specific polymerase chain reaction enhance specificity of detecting STAT1 methylation

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    AbstractObjectiveSignal transducer and activator of transcription (STAT)1 is a key tumor suppressor, which is always methylated in a variety of human cancers. However, nonspecific primers for the detection of specific promoter hypermethylation of STAT1 gene can lead to false-positive or false-negative results for gene methylation.Materials and MethodsWe designed new primers for the detection of STAT1 methylation and compared the sensitivities and specificities of these new primers with prior published primers by methylation-specific polymerase chain reaction (PCR) from ovarian clear cell carcinomas. The mRNA expression levels of STAT1 in these cancerous tissues were also evaluated by reverse-transcriptase PCR and correlated with the results of promoter methylation of STAT1 gene.ResultsNine (39%) of the 23 samples detected by the new primers and 13 samples (56%) detected by prior published primers showed STAT1 methylation. A direct DNA sequencing test revealed that four of the 13 samples (30.8%) showed false positivity for STAT1 methylation using the prior published primers. In contrast, none of the nine samples was false-positive for the detection of STAT1 methylation using the new primers. The new primers for the detection of STAT1 methylation showed 100% specificity and 100% sensitivity without false positivity.ConclusionSpecific primers for methylation-specific PCR are mandatory for the accurate detection of STAT1 gene methylation. Besides, specific primers can generate correct interpretation of STAT1 gene methylation, and its correlation with the clinicopathological characteristics and outcome of cancer patients

    The Inhibitory Effect of Ellagic Acid on Cell Growth of Ovarian Carcinoma Cells

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    Ellagic acid (EA) is able to inhibit the growth of several cancer cells; however, its effect on human ovarian carcinoma cells has not yet been investigated. Ovarian carcinoma ES-2 and PA-1 cells were treated with EA (10~100 μM) and assessed for viability, cell cycle, apoptosis, anoikis, autophagy, and chemosensitivity to doxorubicin and their molecular mechanisms. EA inhibited cell proliferation in a dose- and time-dependent manner by arresting both cell lines at the G1 phase of the cell cycle, which were from elevating p53 and Cip1/p21 and decreasing cyclin D1 and E levels. EA also induced caspase-3-mediated apoptosis by increasing the Bax : Bcl-2 ratio and restored anoikis in both cell lines. The enhancement of apoptosis and/or inhibition of autophagy in these cells by EA assisted the chemotherapy efficacy. The results indicated that EA is a potential novel chemoprevention and treatment assistant agent for human ovarian carcinoma

    Genotoxic Klebsiella pneumoniae in Taiwan

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    Colibactin is a nonribosomal peptide-polyketide synthesized by multi-enzyme complexes encoded by the pks gene cluster. Colibactin-producing Escherichia coli have been demonstrated to induce host DNA damage and promote colorectal cancer (CRC) development. In Taiwan, the occurrence of pyogenic liver abscess (PLA) has been suggested to correlate with an increasing risk of CRC, and Klebsiella pneumoniae is the predominant PLA pathogen in Taiwan
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