IR Field Research Articles

Photoionization of Xe and Xe@C60 from the 4d shell in RABBITT fields

We consider photoemission from the $4d$ shell of the free Xe and encapsulated Xe@${\mathrm{C}}_{60}$ atoms by ionizing XUV and probing IR fields typical for a RABBITT (reconstruction of attosecond beating by interference of two-photon transitions) measurement. Our theoretical model is based on the numerical solution of the time-dependent Schr\odinger equation in the single-active-electron approximation. The fullerene ${\mathrm{C}}_{60}$ cage is represented by a finite-width well potential. We test our model against an analogous set of nonrelativistic [Phys. Rev. A 89, 053424 (2014)] and relativistic [Phys. Rev. A 96, 053407 (2017)] calculations for the $4d$ shell of Xe and Xe@${\mathrm{C}}_{60}$ driven by a continuous XUV field. Based on this verification, we make predictions for the total ionization probability, angular anisotropy $\ensuremath{\beta}$ parameter, and the angular-dependent atomic time delay ${\ensuremath{\tau}}_{a}$ from the threshold to several hundred eV of excess energy.

RG flows and cascades of Lif4(2)\u2009\xd7\u2009S1\u2009\xd7\u2009S5 vacua

The (F1,D2,D8) brane configuration produces Lif4(2) × S1 × S5 Lifshitz vacua supported by ‘massive’ B-field. We present exact deformations of this system under which new massless B-modes of strings also get excited. Due to these massless modes the deformed solutions flow to conformally Lif4(3) × S1 × S5 vacua in the IR. The latter types are supersymmetric solutions of ordinary type IIA theory. The massive and massless Bμν modes segregate out in the IR. We confirm that the massive B mode and cosmological constant indeed decouple from the theory rendering the IR field dynamics controlled by massless fields only. A similar effect is observed on the UV side of the flow where a relativistic regime reappears. We also present ‘cascading’ Lifshitz vacua in which dynamical exponent has integral jumps along the flow; Lif4(3) → Lif4(2) → Lif4(1). The critical Lif4(2) theory separates ‘deconfining’ Lif4(3) IR theory from the confining Yang-Mills phase in UV.

Attosecond coherent control of oxygen dissociation by XUV-IR laser fields using three-dimensional momentum imaging

Author(s): Ranitovic, P; Sturm, FP; Tong, XM; Wright, TW; Ray, D; Zalyubovskya, I; Shivaram, N; Belkacem, A; Slaughter, DS; Weber, T | Abstract: We have performed ultrafast three-dimensional ion momentum imaging spectroscopy on the dissociative single ionization of oxygen molecules using attosecond pulse trains with a broad energy spectrum of 5-30 eV. High-resolution momentum imaging allows clear identification of vibrational structures corresponding to the predissociation of highly excited cationic states. By adding a pump infrared field that is synchronized with and polarized orthogonally to the XUV pulse train, and an additional probe IR field, we demonstrate how the yield of O+ ions can be steered between different dissociation channels by coherently controlling the coupling between multiple O2+∗ electronic states on an attosecond time scale. Time-dependent calculations in a single active electron approximation allow a qualitative analysis of ion yields for two orientations of the molecular axis.

La Economía Política Internacional en el campo de las Relaciones Internacionales argentinas

Este trabajo busca responder a la pregunta acerca de cuáles han sido los principales aportes de la Economía Política Internacional (EPI) al devenir histórico del campo intelectual de las Relaciones Internacionales (RI) en Argentina. El Trabajo se inscribe en dar respuesta a una pregunta más amplia acerca del proceso de constitución del campo de las ri como disciplina académica autónoma en Argentina. Se indagará sobre los aportes realizados por la epi, especialmente, el estructuralismo latinoamericano y el desarrollismo, como espacios de producción teórica y conceptual desde donde se construye parte del pensamiento sobre la realidad internacional. El objetivo del trabajo girará en torno a reconstruir la agenda de epi y su contribución al desarrollo de las ri argentinas mediante la observación y análisis de los principales autores y conceptos, las instituciones que han servido como espacios de producción de conocimiento y las revistas especializadas que actuaron como plataformas para la difusión de temas e ideas.

Simulation of angular-resolved RABBITT measurements in noble-gas atoms

We simulate angular resolved RABBITT (Reconstruction of Attosecond Beating By Interference of Two-photon Transitions) measurements on valence shells of noble gas atoms (Ne, Ar, Kr, and Xe). Our non-perturbative numerical simulation is based on solution of the time-dependent Schr\"odinger equation for a target atom driven by an ionizing XUV and dressing IR fields. From these simulations we extract the angular dependent magnitude and phase of the RABBITT oscillations and deduce the corresponding angular anisotropy {\beta} parameter and Wigner time delay ${\tau}_W$ for the single XUV photon absorption which initiates the RABBITT process. Said {\beta} and ${\tau}_W$ parameters are compared with calculations in the random phase approximation with exchange (RPAE) which includes inter-shell correlation. This comparison is used to test various effective potentials employed in the one-electron TDSE. In lighter atoms (Ne and Ar), several effective potentials are found to provide accurate simulation of RABBITT measurements for a wide range of photon energies up to 100 eV above the valence shell threshold. In heavier atoms (Kr and Xe), the onset of strong correlation with the d-shell restricts the validity of the single active electron approximation to several tens of eV above the valence shell threshold.

Turning Temporal: a Discourse of Time in IR

Recent studies dedicated to time in IR often begin with the claim that the field has long relegated time to a background position, and only recently begun taking the concept seriously, with many fruitful insights. In this article, I refuse this interpellation to ‘take time seriously’, instead proposing we read these claims as part of a discourse, that is, a set of regularities through which we organise and distribute time as an object of knowledge in IR, and through which we come to govern ourselves and others. First, by engaging works of the ‘temporal turn’, I describe four procedures through which the discourse of time in IR is organised: opposing conceptual fields, scaling objects, naturalising and repressing desires, and strategic inverting. Second, I argue this reading shows that the temporal turn might ultimately fall short of realising its proclaimed aims. However, and third, I propose we take this not as a failure, but as the effective working of the discourse. Fourth, in doing so, I suggest the discourse of time effectively ‘changes the subject’ in terms of both the problems posed and the subjectivities constituted in relation to them – in the field of IR, but possibly also more broadly.

Theorizing international security regimes: a power-analytical approach

This article seeks to develop alternative ways to conceptually grasp international prohibition/regulatory regimes. It attempts to go beyond existing, and piecemeal, analysis of regimes within the intellectual field of IR based on conventional grand/mid-range theorization. It is argued that traditional theorization of regimes fashioned as IR theory has hindered, rather than helped, to understand regimes in their complexities, vagaries, and in terms of various forces simultaneously involved. The article answers a question of how to strike a balance between theoretical eclecticism, which is believed to be vital for a comprehensive analysis of security regimes, and the need to have a uniting device to organize such research. It is for these reasons that a power-analytical approach utilizing four types of powers—productive, structural, institutional, and compulsory—is used, and its advantages for regime analysis are flagged. The value added of such an advancement lies in international security regimes being understood more plastically than through conventional lenses. Specifically, they are approached as intertwined sets of normative discourses, political structures (anarchies, hierarchies, and heterarchies), and agencies through which power operates within a given security issue area with a regulatory effect. Specific renderings of discourses and heterarchies establish channels through which sociopolitical and economic privileges get distributed; they create structural relations among actors with a possibility of their reversal or rearticulation; and they build up, challenge, and relocate walls of legal obligations.

Quasi-phase-matching of high-order harmonics in plasma plumes: theory and experiment.

We theoretically analyze the phase-matching of high-order harmonic generation (HHG) in multi-jet plasmas and find the harmonic orders for which the quasi-phase-matching (QPM) is achieved depending on the parameters of the plasma and the generating beam. HHG by single- and two-color generating fields is analyzed. The QMP is studied experimentally for silver, indium and manganese plasmas using near IR and mid-IR laser fields. The theory is validated by comparison with our experimental observations, as well as published experimental data. In particular, the plasma densities and the harmonic phase coefficients reconstructed from the observed harmonic spectra using our theory agree with the corresponding parameters found using other methods. Our theory allows defining the plasma jet and the generating field properties, which can maximize the HHG efficiency due to QPM.

Report on the Second Workshop on Supporting Complex Search Tasks

There is broad consensus in the field of IR that search is complex in many use cases and applications, both on the Web and in domain-specific collections, and both in our professional and in our daily life. Yet our understanding of complex search tasks, in comparison to simple look up tasks, is fragmented at best. The workshop addressed many open research questions: What are the obvious use cases and applications of complex search? What are essential features of work tasks and search tasks to take into account? And how do these evolve over time? With a multitude of information, varying from introductory to specialized, and from authoritative to speculative or opinionated, when should which sources of information be shown? How does the information seeking process evolve and what are relevant differences between different stages? With complex task and search process management, blending searching, browsing, and recommendations, and supporting exploratory search to sensemaking and analytics, UI and UX design pose an overconstrained challenge. How do we know that our approach is any good? Supporting complex search tasks requires new collaborations across the whole field of IR, and the proposed workshop brought together a diverse group of researchers to work together on one of the greatest challenges of our field. The workshop featured three main elements. First, two keynotes, one on the complexity of meaningful interactive IR evaluation by Mark Hall and one on the types of search complexity encountered in real-world applications by Jussi Karlgren. Second, a lively boaster and poster session in which seven contributed papers were presented. Third, three breakout groups discussed concrete ideas on: (1) search context and tasks, (2) search process, and (3) evaluation of complex search tasks. There was an general feeling that the discussion made progress, and built new connections between related strands of research in IR

Angle-dependent time delay in two-color XUV+IR photoemission of He and Ne

We solve the time-dependent Schr\odinger equation for a noble gas atom (He and Ne) driven by an ionizing XUV and dressing IR fields. From this solution we deduce an angular dependence of the photoemission time delay as measured by the RABBITT (reconstruction of attosecond beating by interference of two-photon transitions) technique. We use a recent angle-resolved RABBITT measurement on helium [S. Heuser et al., Phys. Rev. A 94, 063409 (2016)] to test and calibrate our theoretical model. Based on this calibration, we find no significant difference between the time delay in He measured in the angle-integrated RABBITT experiments [C. Palatchi et al., J. Phys. B 47, 245003 (2014) and D. Gu\'enot et al., J. Phys. B 47, 245602 (2014)] and measured or calculated in the polarization axis direction. The angular dependence of the photoemission time delay of Ne is shown to be qualitatively different from He because of the different orbital character of the valence $2p$ orbital. The angular momentum projection dependence of the time delay in Ne is also investigated.

A Method For Achieving Super Resolution Vibrational Sum-Frequency Generation Microscopy By Structured Illumination

A scheme was proposed to achieve wide-field vibrational sum-frequency generation (SFG) microscopy with subdiffraction-limited resolution in one dimension. In this approach, samples are illuminated with a structured visible field and a uniform IR field to induce vibrational sum-frequency generation. With five raw images acquired at five different phases of the visible stripe pattern, a super-resolved vibrational SFG (SR-SFG) image with the resolution triple to that of the original can be reconstructed. Theoretical framework describing the coherent image formation and reconstruction scheme for the SR-SFG imaging system was derived and carried out with numerical simulations to investigate its imaging performance. With a typical imaging system, the lateral resolution was improved from 390 nm of the conventional SFG imaging system, to around 130 nm of the SR-SFG imaging system.

Laser control over the ultrafast Coulomb explosion of N22+ after Auger decay: A quantum-dynamics investigation

By theoretical calculation, we demonstrate the possibility to control and partially suppress the Coulomb explosion of ${\mathrm{N}}_{2}$ molecules after core-level photoionization by an x-ray laser and subsequent Auger decay. This is achieved by means of a femtosecond infrared laser pulse interacting with the ${\mathrm{N}}_{2}{}^{2+}$ dication produced by the x-ray pulse. Suppression of molecular fragmentation requires few-femtosecond IR pulses interacting with the system either during or shortly after the arrival of the x-ray pulse. The IR pulse suppresses fragmentation mostly by optically coupling the electronic routes to ultrafast molecular dissociation with electronic channels able to support long-lived vibrational resonances. The effect is strongly dependent on the orientation of the molecule with respect to the polarization axis of the IR field. Our calculations are motivated by x-ray pump--IR probe experiments performed at an x-ray free-electron laser [J. M. Glownia et al., Opt. Express 18, 17620 (2010)], where only enhancement of ${\mathrm{N}}_{2}{}^{2+}$ fragmentation as a function of the pump-probe delay time was reported. The opposite effect reported here becomes apparent when the various electronic channels are considered separately. In practice, this corresponds to a coincident measurement of the energy of the ejected Auger electron.

A neural controller for online laser power adjustment during the heat therapy process in the presence of nanoparticles.

The present research evaluated the efficiency of a control approach to control the temperature of a breast tumor mass in the presence of nanoparticles exposed to laser radiation. However, if the radiation is carried out in open loop manner it may result in excessive temperature rise healthy cells that exist in the vicinity of tumor's cells. This may lead to the death of healthy cells. So, using closed loop control methods is necessary to guarantee the preservation of healthy cells during the period of radiation. Therefore, in this study, an artificial neural network was trained as a controller. In other words, the trained neural network adjusted the laser power over a period of time in such a way that the temperature in the center of the tumor reached the desired level with an appropriate temporal behavior. The difference between the real temperature of the tumor and the desired temperature of it is the controller input, while the controller output determined the amount of laser power. The simulation studies were carried out using an appropriate physiological model in the presence of nanoparticles. First, Schrödinger equations were solved followed by the effective mass equation. Afterward the optimum number of nanoparticles to be used in the IR field was calculated. Next, the important electro-optical features related to the nanostructure, such as the absorption continuum and reflection continuum had been calculated. The neural network proposed controller was then evaluated through other simulation studies in the tumor mass model. The results showed a promising performance by the trained artificial neural network in adjusting radiated laser power for the desired temperature increase in the center of a tumor mass.

Black hole singularity, generalized (holographic) c-theorem and entanglement negativity

In this paper we revisit the question that in what sense empty AdS5 black brane geometry can be thought of as RG-flow. We do this by first constructing a holographic c-function using causal horizon in the black brane geometry. The UV value of the c-function is aUV and then it decreases monotonically to zero at the curvature singularity. Intuitively, the behavior of the c-function can be understood if we recognize that the dual CFT is in a thermal state and thermal states are effectively massive with a gap set by the temperature. In field theory, logarithmic entanglement negativity is an entanglement measure for mixed states. For example, in two dimensional CFTs at finite temperature the renormalized entanglement negativity of an interval has UV (Low-T) value cUV and IR (High-T) value zero. So this is a potential candidate for our c-function. In four dimensions we expect the same thing to hold on physical grounds. Now since the causal horizon goes behind the black brane horizon the holographic c-function is sensitive to the physics of the interior. Correspondingly the field theory c-function should also contain information about the interior. So our results suggest that high temperature (IR) expansion of the negativity (or any candidate c-function) may be a way to probe part of the physics near the singularity. Negativity at finite temperature depends on the full operator content of the theory and so perhaps this can be done in specific cases only.The existence of this c-function in the bulk is an extreme example of the paradigm that space-time is built out of entanglement. In particular the fact that the c-function reaches zero at the curvature singularity correlates the two facts: loss of quantum entanglement in the IR field theory and the end of geometry in the bulk which in this case is the formation of curvature singularity.

Selective bond dissociation of HOD molecule by optimally designed polychromatic IR+UV pulse: a genetic-algorithm-based study

ABSTRACTA theoretical investigation of selective bond dissociation of O–H or O–D bond of HOD molecule is carried out by optimally designed electromagnetic field where optimisation is performed by Genetic Algorithm (GA). Two strategies depending upon the objective function and variable space for optimisation have been followed to achieve selective photodissociation. In Strategy I flux along a particular channel (JH + O-D/JD + O-H) in the repulsive excited state of HOD is considered in defining the objective function with a polychromatic IR pulse of eight components and a UV radiation of two components being optimally found out by GA. The polychromatic IR pulse distributes the population among the low quanta vibrational states of O–H or O–D stretching mode in ground electronic state and the subsequent UV pulse transfers the population to the excited state where photodissociation occurs. According to the direction of population along O–H or O–D stretch in ground electronic state, fluxes in the channels may be expected. We have obtained a maximum value of 92.38% and 74.12% along JH + O-D and JD + O-H channels, respectively. The Strategy II is the conventional strategy of selective vibrational excitation followed by population transfer to excited state by single UV pulse. In this case, the polychromatic IR fields are optimised by GA to achieve selective vibrational excitation on |1, 0⟩, |2, 0⟩, |0, 1⟩ and |0, 2⟩ states and the matching single UV pulse is fired for electronic excitation. The first two states correspond to the O–H stretch and population transfer from these states to excited state result in predominant flux along H+O–D channel and similar scheme from the last two states result in D+O–H dissociation as they are effectively of O–D character. The best values of JH + O-D and JD + O-H are 86.91% and 65.94% obtained by using Strategy II.

Towards the analysis of attosecond dynamics in complex systems.

We study from a theoretical perspective the ionization of molecules and clusters induced by irradiation of a combined two-color laser field consisting of a train of attosecond XUV pulses in the presence of an IR field. We use time-dependent density-functional theory (TDDFT) in real time and real space as a theoretical tool. The calculated results are compared to experimental data when available. We also compare TDDFT with results obtained using a time-dependent Schrödinger equation (TDSE), which is well suited to simple systems while TDDFT allows dealing with more complex molecules and clusters. As a key observable, we study ionization versus delay time of the XUV pulses with respect to the IR background pulse. Experiments in simple atoms (He and Ar) show a regular modulation of this signal with half the IR period. This feature is recovered by TDDFT as well as by the TDSE (although total ionization differs by an order of magnitude). As more complex systems, we consider a C3 chain molecule and Na clusters. Here we encounter a different picture as the ionization signal develops a more involved pattern with several peaks per half IR period and as the TDSE produces a different pattern to TDDFT. Both effects could be related to the appearance of strong resonance modes in these more complex systems.

Magnetism, hysteresis cycle, and Ir-substitution doping of Sr2CrIrO6 double perovskite: A Monte Carlo simulation

Iridium-based double perovskite (DP) Sr2CrIrO6 is expected to have the highest Curie temperatures (Tc) among all DPs and a high spin-polarization at room temperature, thanks to the more extended 5d orbitals of Ir, which makes it potential candidate in spintronic applications. Several publications have appeared in recent years documenting Ir-based double perovskites, but very few have explored the promising compound Sr2CrIrO6. In this paper, a Monte Carlo simulation has been carried out in the framework of Ising model to make an exploratory study of Sr2CrIrO6. Thermal magnetization, magnetic susceptibility, internal energy and specific heat have been studied. Effect of crystal field of Ir on the magnetic properties has been explored. Magnetic hysteresis cycle has been studied in relation to the exchange coupling values. Effects of Ir-substitution doping by Os “Sr2CrIrxOs1−xO6” and by Re “Sr2CrIrxRe1−xO6” (0.1≤x≤0.5) on the magnetic behavior have been investigated.

Simulation of X-ray transient absorption for following vibrations in coherently ionized F2 molecules

Femtosecond and attosecond X-ray transient absorption experiments are becoming increasingly sophisticated tools for probing nuclear dynamics. In this work, we explore and develop theoretical tools needed for interpretation of such spectra,in order to characterize the vibrational coherences that result from ionizing a molecule in a strong IR field. Ab initio data for F2 is combined with simulations of nuclear dynamics, in order to simulate time-resolved X-ray absorption spectra for vibrational wavepackets after coherent ionization at 0K and at finite temperature. Dihalogens pose rather difficult electronic structure problems, and the issues encountered in this work will be reflective of those encountered with any core–valence excitation simulation when a bond is breaking. The simulations reveal a strong dependence of the X-ray absorption maximum on the locations of the vibrational wave packets. A Fourier transform of the simulated signal shows features at the overtone frequencies of both the neutral and the cation, which reflect spatial interferences of the vibrational eigenstates. This provides a direct path for implementing ultrafast X-ray spectroscopic methods to visualize coherent nuclear dynamics.

Coherent forward scattering of γ-ray and XUV radiation in the medium with the modulated quasi-resonant transition

We establish a close physical analogy between coherent forward scattering of γ-ray radiation in the vibrating quasi-resonant nuclear absorber and the XUV field propagation in the quasi-resonant atomic medium in the presence of the moderately strong IR field. We prove that both processes, under certain conditions, are described by similar Maxwell–Bloch equations for a two-level medium with modulated parameters of the resonant transition. It results in similar transformation of both γ-ray and XUV fields at the exit from the medium, fully determined by the characteristics of applied modulation and spectral content of the incident fields. We find an appropriate analytical solution describing transformation of the electromagnetic field as a result of its propagation in the modulated medium. We show, in particular, that recently observed effects of (i) suppressed resonant absorption in coherent γ-ray scattering of vibrating absorber and (ii) ionization rate modulation in IR pump–XUV probe experiments, present themselves as different manifestations of the same general physical phenomenon of modulation induced transparency (MIT). That transparency is induced by modulating the parameters of the resonant transition. While only partial MIT was observed so far, we suggest certain conditions for conducting some realistic experiments, which should demonstrate nearly 100% transparency in both processes.

Phosphorylated Codonopsis pilosula polysaccharide could inhibit the virulence of duck hepatitis A virus compared with Codonopsis pilosula polysaccharide

To screen effective anti-duck hepatitis A virus (DHAV) drugs, we applied STMP-STPP method to prepare phosphorylated Codonopsis pilosula polysaccharide (pCPPS), the phosphorylation-modified product of Codonopsis pilosula polysaccharide (CPPS). The IR spectrum and field emission scanning electron microscope (FE-SEM) were subsequently used to analyze the structure of pCPPS. Several tests were conducted to compare the anti-DHAV activities of CPPS and pCPPS. The MTT method was used to compare the effect of the drugs on DHAV-infected duck embryonic hepatocytes (DEHs), and the Reed-Muench assay was employed to observe changes in the virulence of DHAV. We also applied real-time PCR to examine the relationship between virus replication and the expression of IFN-β. The results indicated that CPPS could not inhibit the replication of DHAV. In contrast, pCPPS increased the virus TCID50, inhibited viral replication and, accordingly, increased the survival rate of DEHs infected with DHAV. Because DHAV induced the expression of IFN-β, and the IFN-β expression level was positively associated with the number of DHAV, the reduction of IFN-β expression levels after pCPPS treatment demonstrated a decrease in the number of virus particles. These results indicated that pCPPS, which reduces the number of DHAV, was more effective than CPPS in anti-DHAV activity.