Achieving High Substitutional Incorporation in Mn-Doped Graphene.

Despite its broad potential applications, substitution of carbon by transition metal atoms in graphene has so far been explored only to a limited extent. We report the realization of substitutional Mn doping of graphene to a record high atomic concentration of 0.5%, which was achieved using ultralow-energy ion implantation. By correlating the experimental data with the results of ab initio Born-Oppenheimer molecular dynamics calculations, we infer that direct substitution is the dominant mechanism of impurity incorporation. Thermal annealing in ultrahigh vacuum provides efficient removal of surface contaminants and additional implantation-induced disorder, resulting in Mn-doped graphene that, aside from the substitutional Mn impurities, is essentially as clean and defect-free as the as-grown layer. We further show that the Dirac character of graphene is preserved upon substitutional Mn doping, even in this high concentration regime, making this system ideal for studying the interaction between Dirac conduction electrons and localized magnetic moments. More generally, these results show that ultralow energy ion implantation can be used for controlled functionalization of graphene with substitutional transition-metal atoms, of relevance for a wide range of applications, from magnetism and spintronics to single-atom catalysis.

Isomer-specific photofragmentation of C3H3+ at the carbon K-edge.

Individual fingerprints of different isomers of C3H3+ cations have been identified by studying photoionization, photoexcitation, and photofragmentation of C3H3+ near the carbon K-edge. The experiment was performed employing the photon-ion merged-beams technique at the photon-ion spectrometer at PETRA III (PIPE). This technique is a variant of near-edge X-ray absorption fine-structure spectroscopy, which is particularly sensitive to the 1s → π* excitation. The C3H3+ primary ions were generated by an electron cyclotron resonance ion source. C3Hn2+ product ions with n = 0, 1, 2, and 3 were observed for photon energies in the range of 279.0 eV to 295.2 eV. The experimental spectra are interpreted with the aid of theoretical calculations within the framework of time-dependent density functional theory. To this end, absorption spectra have been calculated for three different constitutional isomers of C3H3+. We find that our experimental approach offers a new possibility to study at the same time details of the electronic structure and of the geometry of molecular ions such as C3H3+.

Optimization of synchrotron radiation parameters using swarm intelligence and evolutionary algorithms.

Alignment of each optical element at a synchrotron beamline takes days, even weeks, for each experiment costing valuable beam time. Evolutionary algorithms (EAs), efficient heuristic search methods based on Darwinian evolution, can be utilized for multi-objective optimization problems in different application areas. In this study, the flux and spot size of a synchrotron beam are optimized for two different experimental setups including optical elements such as lenses and mirrors. Calculations were carried out with the X-ray Tracer beamline simulator using swarm intelligence (SI) algorithms and for comparison the same setups were optimized with EAs. The EAs and SI algorithms used in this study for two different experimental setups are the Genetic Algorithm (GA), Non-dominated Sorting Genetic Algorithm II (NSGA-II), Particle Swarm Optimization (PSO) and Artificial Bee Colony (ABC). While one of the algorithms optimizes the lens position, the other focuses on optimizing the focal distances of Kirkpatrick-Baez mirrors. First, mono-objective evolutionary algorithms were used and the spot size or flux values checked separately. After comparison of mono-objective algorithms, the multi-objective evolutionary algorithm NSGA-II was run for both objectives - minimum spot size and maximum flux. Every algorithm configuration was run several times for Monte Carlo simulations since these processes generate random solutions and the simulator also produces solutions that are stochastic. The results show that the PSO algorithm gives the best values over all setups.

Association Between Domain-Specific Physical Activity and Chronic Low Back Pain in Community-Dwelling Older Adults: A Cross-Sectional Study.

To investigate the association between physical activity (PA) domains and chronic low back pain (LBP) in older adults. A cross-sectional study where sociodemographic, behavioral, and health variables; PA; and presence of chronic LBP were collected. Higher scores of PA defined the "more active" participants. Binary logistic regression was used to test the association between PA domains and chronic LBP. A total of 516 participants were included. The mean age was 71.8 (95% confidence interval, CI, [71.1, 72.5]) years, and 29%, 27%, 25%, and 31% were identified as "more active" in the household, sports, leisure-time, and total PA domains, respectively. "More active" participants in sports (odds ratio = 0.62, 95% CI [0.40, 0.97]), leisure-time (odds ratio = 0.54, 95% CI [0.35, 0.85]) and total (odds ratio = 0.60, 95% CI [0.39, 0.92]) PA domains were less likely to report chronic LBP. High levels of sports, leisure-time, and total PA were inversely associated with chronic LBP.

Charge-induced chemical dynamics in glycine probed with time-resolved Auger electron spectroscopy.

In the present contribution, we use x-rays to monitor charge-induced chemical dynamics in the photoionized amino acid glycine with femtosecond time resolution. The outgoing photoelectron leaves behind the cation in a coherent superposition of quantum mechanical eigenstates. Delayed x-ray pulses track the induced coherence through resonant x-ray absorption that induces Auger decay. Temporal modulation of the Auger electron signal correlated with specific ions is observed, which is governed by the initial electronic coherence and subsequent vibronic coupling to nuclear degrees of freedom. In the time-resolved x-ray absorption measurement, we monitor the time-frequency spectra of the resulting many-body quantum wave packets for a period of 175 fs along different reaction coordinates. Our experiment proves that by measuring specific fragments associated with the glycine dication as a function of the pump-probe delay, one can selectively probe electronic coherences at early times associated with a few distinguishable components of the broad electronic wave packet created initially by the pump pulse in the cation. The corresponding coherent superpositions formed by subsets of electronic eigenstates and evolving along parallel dynamical pathways show different phases and time periods in the range of ( - 0.3 ± 0.1 ) π ≤ ϕ ≤ ( 0.1 ± 0.2 ) π and 18.2 - 1.4 + 1.7 ≤ T ≤ 23.9 - 1.1 + 1.2 fs. Furthermore, for long delays, the data allow us to pinpoint the driving vibrational modes of chemical dynamics mediating charge-induced bond cleavage along different reaction coordinates.

X-Ray absorption spectroscopy of H3O.

We report the X-ray absorption of isolated H3O+ cations at the O 1s edge. The molecular ions were prepared in a flowing afterglow ion source which was designed for the production of small water clusters, protonated water clusters, and hydrated ions. Isolated H2O+ cations have been analyzed for comparison. The spectra show significant differences in resonance energies and widths compared to neutral H2O with resonances shifting to higher energies by as much as 10 eV and resonance widths increasing by as much as a factor of 5. The experimental results are supported by time-dependent density functional theory calculations performed for both molecular cations, showing a good agreement with the experimental data. The spectra reported here could enable the identification of the individual molecules in charged small water clusters or liquid water using X-ray absorption spectroscopy.

Electronic quantum coherence in glycine molecules probed with ultrashort x-ray pulses in real time.

Here, we use x-rays to create and probe quantum coherence in the photoionized amino acid glycine. The outgoing photoelectron leaves behind the cation in a coherent superposition of quantum mechanical eigenstates. Delayed x-ray pulses track the induced coherence through resonant x-ray absorption that induces Auger decay and by photoelectron emission from sequential double photoionization. Sinusoidal temporal modulation of the detected signal at early times (0 to 25 fs) is observed in both measurements. Advanced ab initio many-electron simulations allow us to explain the first 25 fs of the detected coherent quantum evolution in terms of the electronic coherence. In the kinematically complete x-ray absorption measurement, we monitor its dynamics for a period of 175 fs and observe an evolving modulation that may implicate the coupling of electronic to vibronic coherence at longer time scales. Our experiment provides a direct support for the existence of long-lived electronic coherence in photoionized biomolecules.

Revealing noncollinear magnetic ordering at the atomic scale via XMCD.

Mass-selected V and Fe monomers, as well as the heterodimer [Formula: see text], were deposited on a Cu(001) surface. Their electronic and magnetic properties were investigated via X-ray absorption (XAS) and X-ray magnetic circular dichroism (XMCD) spectroscopy. Anisotropies in the magnetic moments of the deposited species could be examined by means of angle resolving XMCD, i.e. changing the X-ray angle of incidence. A weak adatom-substrate-coupling was found for both elements and, using group theoretical arguments, the ground state symmetries of the adatoms were determined. For the dimer, a switching from antiparallel to parallel orientation of the respective magnetic moments was observed. We show that this is due to the existence of a noncollinear spin-flop phase in the deposited dimers, which could be observed for the first time in such a small system. Making use of the two magnetic sublattices model, we were able to find the relative orientations for the dimer magnetic moments for different incidence angles.

Evidence for the coexistence of spin-glass and ferrimagnetic phases in BaFe12O19 due to basal plane freezing.

We present here the results of low-temperature magnetization and X-ray magnetic circular dichroism studies on the single crystals of BaFe12O19 which reveal for the first time the emergence of a spin glass phase, in coexistence with a long-range ordered ferrimagnetic phase, due to the freezing of the basal plane spin component.

Absorption spectra at the iodine 3d ionisation threshold following the CHxI+ (x = 0-3) cation sequence.

Yields of atomic iodine Iq+ (q≥ 2) fragments resulting from photoexcitation and photoionisation of the target cations CHxI+ (x = 0-3) have been measured in the photon-energy range 610 eV to 670 eV, which comprises the threshold for iodine 3d ionisation. The measured ion-yield spectra show two strong and broad resonance features due to the excitation of the 3d3/2,5/2 electrons into εf states similar to atomic iodine. In the 3d pre-edge range, electrons are excited into molecular orbitals consisting of iodine, carbon, and hydrogen atomic orbitals. These transitions have been identified by comparison with literature data and by simulations using time-dependent density functional theory (TDDFT) with the KMLYP functional. The ion-yield spectrum for CH3I+ resembles the spectrum of IH+ [Klumpp et al., Phys. Rev. A, 2018, 97, 033401] because the highest occupied molecular orbitals (HOMO) of the H and CH3 fragments both contain a single vacancy, only. For the molecular cations with higher number of vacancies in the valence molecular orbitals CHxI+ (x = 0-2), a stronger hybridisation of the molecular orbitals occurs between the organic fragment and the iodine resulting in a change of bonding from a single σ bond in CH3I+ to a triple bond including two π orbitals in CI+. This is reflected in the resonance energies of the observed absorption lines below the iodine 3d excitation threshold.

Inner-shell X-ray absorption spectra of the cationic series NHy+ (y = 0-3).

Ion yields following X-ray absorption of the cationic series NHy+ (y = 0-3) were measured to identify the characteristic absorption resonances in the energy range of the atomic nitrogen K-edge. Significant changes in the position of the absorption resonances were observed depending on the number of hydrogen atoms bound to the central nitrogen atom. Configuration interaction (CI) calculations were performed to obtain line assignments in the frame of molecular group theory. To validate the calculations, our assignment for the atomic cation N+, measured as a reference, was compared with published theoretical and experimental data.

Blood flow restriction training promotes hypotensive effect in hypertensive middle-age men / Efecto hipotensor producido por entrenamiento de restricción vascular sanguíneo en hipertensos de mediana edad

Objectives: The purposes of this study were a) to analyze the hemodynamic responses of two methods of resistance training (vascular occlusion vs. traditional) and, b) to demonstrate the effectiveness of vascular occlusion training method on the regulation of blood pressure in hypertensive subjects. Methods: Ten men of middle age (44.9±5.1 years, 83.7±12. kg, 174.1±8.1cm) performed two different protocols of resistance exercises (3 sets until concentric failure; leg press exercise; 60 sec pause between sets): a) with blood flow restriction (30% of 1RM intensity) and b) high intensity exercise (70% of 1RM intensity). Middle thigh muscle circumference was estimated and hemodynamic variables (heart rate, systolic and diastolic blood pressure) were measured before, immediately after and every 10 min (until 60 min) post exercise. The rate of perceived exertion was also utilized after exercise protocol. All subjects were encouraged not to perform the Valsalva maneuver. Results: Both protocols showed a significant reduction of systolic, diastolic and mean arterial blood pressure and heart rate post 10 until 60 min compared to values immediately post exercise (p<0.05). The blood flow restriction group showed a significant reduction (p<0.05) of diastolic blood pressure 20 min post-exertion time compared to rest values. In addition, the magnitude of the effect size about diastolic blood pressure revealed a large magnitude of effect at the 20' and 30 post-effort in the blood flow restriction group. Conclusion: Blood flow restriction protocol promoted a hypotensive effect during 60 min after it is realization

Objetivos: Los objetivos de este estudio fueron: a) analizar las respuestas hemodinámicas de dos métodos de entrenamiento de resistencia (oclusión vascular versus tradicional) y b) demostrar la efectividad del método de entrenamiento de oclusión vascular en la regulación de la presión arterial en sujetos hipertensos. Métodos: Diez hombres de mediana edad (44,9±5,1 años, 83,7±12 kg, 174,1±8,1 cm) realizaron dos protocolos diferentes de ejercicios de fuerza (3 series hasta el fallo concéntrico, ejercicio de ejercicios de pierna, pausa de 60 segundos entre series): a) Con restricción del flujo sanguíneo (30% de intensidad de 1RM) y b) ejercicio de alta intensidad (70% de intensidad de 1RM). Se estimó la circunferencia muscular media del muslo y se midieron las variables hemodinámicas (frecuencia cardíaca, presión arterial sistólica y diastólica) antes, inmediatamente después y cada 10 min (hasta 60 minutos) después del ejercicio. La escala de esfuerzo percibido también se utilizó después del protocolo de ejercicio. Se animó a todos los sujetos a no realizar la maniobra de Valsalva. Resultados: Ambos protocolos mostraron una reducción significativa de la presión arterial sistólica, diastólica y media ya frecuencia cardíaca post 10 hasta 60 min en comparación con los valores inmediatamente después del ejercicio (p<0.05). El grupo de restricción del flujo sanguíneo mostró una reducción significativa (p<0.05) de la presión arterial diastólica 20 minutos después del esfuerzo en comparación con los valores de reposo. Además, la magnitud del tamaño del efecto sobre la presión arterial diastólica reveló una gran magnitud de efecto a los 20 ‘ y 30’ post-esfuerzo en el grupo de restricción de flujo sanguíneo. Conclusión: El protocolo de restricción del flujo sanguíneo promovió un efecto hipotensor durante 60 minutos después de su realización

Magnetic properties of supported metal atoms and clusters.

Clusters are small systems ranging from a few atoms up to several thousand atoms. They are of high interest in basic research, but also for applications due to their specific electronic, magnetic or chemical properties depending on size and composition. For small clusters, quantum size effects play an important role and specific material properties might be tailored by choosing a special size or composition of the cluster. Here, we review the magnetic properties of adatoms and supported small mass-selected transition-metal clusters in the few-atom limit investigated by x-ray magnetic circular dichroism spectroscopy in the soft x-ray regime. The influence of cluster size, composition, the cluster-surface and intra-cluster interaction on the spin and orbital magnetic moments will be discussed.

The spin and orbital contributions to the total magnetic moments of free Fe, Co, and Ni clusters.

We present size dependent spin and orbital magnetic moments of cobalt (Con (+), 8 ≤ n ≤ 22), iron (Fen (+), 7 ≤ n ≤ 17), and nickel cluster (Nin (+), 7 ≤ n ≤ 17) cations as obtained by X-ray magnetic circular dichroism (XMCD) spectroscopy of isolated clusters in the gas phase. The spin and orbital magnetic moments range between the corresponding atomic and bulk values in all three cases. We compare our findings to previous XMCD data, Stern-Gerlach data, and computational results. We discuss the application of scaling laws to the size dependent evolution of the spin and orbital magnetic moments per atom in the clusters. We find a spin scaling law "per cluster diameter," ∼n(-1/3), that interpolates between known atomic and bulk values. In remarkable contrast, the orbital moments do likewise only if the atomic asymptote is exempt. A concept of "primary" and "secondary" (induced) orbital moments is invoked for interpretation.

Influence of Blood Flow Restriction During Low-Intensity Resistance Exercise on the Postexercise Hypotensive Response.

Low-intensity resistance exercise (RE) combined with blood flow restriction (BFR) has been shown to promote similar increases in strength and hypertrophy as traditional high-intensity RE without BFR. However, the effect of BFR on the acute postexercise hypotensive response has received limited examination. Therefore, the purpose of this study was to compare high-intensity exercise (HIE) vs. low-intensity RE with BFR on the postexercise hypotensive response in normotensive young subjects. Fifteen men (age: 23.4 ± 3.4 years) performed the following 2 experimental protocols in randomized order: (a) 3 sets of biceps curls (BCs) at 80% of 1 repetition maximum (RM) and 120-second rest between sets (HIE protocol) and (b) 3 sets of BCs at 40% of 1RM with BFR and 60-second rest between sets. Analysis of systolic blood pressure (SBP) and diastolic blood pressure (DBP) was conducted for 60 minutes after both protocols. The values for SBP, DBP, and mean blood pressure (MBP) at baseline and postexercise were not significantly different between the HIE vs. the BFR protocol. However, within the BFR protocol, significant decreases (p ≤ 0.05) in SBP occurred at 30 minutes (125.86 ± 9.33 mm Hg) and 40 minutes (125.53 ± 10.19 mm Hg) after exercise when compared with baseline (132.86 ± 9.12 mm Hg) and significant decreases in DBP and MBP occurred at 20 minutes, 30 minutes, and 40 minutes after exercise vs. baseline (p ≤ 0.05). Therefore, we conclude that exercises engaging a relatively small amount of muscle mass, such as the BC (or other similar single joint exercises), might be performed at a lower intensity with BFR to promote a postexercise hypotensive response.

Digital in-line holography with femtosecond VUV radiation provided by the free-electron laser FLASH.

Femtosecond vacuum ultraviolet (VUV) radiation provided by the free-electron laser FLASH was used for digital in-line holographic microscopy and applied to image particles, diatoms and critical point dried fibroblast cells. To realize the classical in-line Gabor geometry, a 1 microm pinhole was used as spatial filter to generate a divergent light cone with excellent pointing stability. At a fundamental wavelength of 8 nm test objects such as particles and diatoms were imaged at a spatial resolution of 620 nm. In order to demonstrate the applicability to biologically relevant systems, critical point dried rat embryonic fibroblast cells were for the first time imaged with free-electron laser radiation.

2p Photoionization of atomic Ni: a comparison with Ni metal and NiO photoionization.

The photoabsorption spectrum of the 2p-3d resonances and the 2p photoelectron spectrum of atomic Ni were investigated both experimentally and theoretically. The analysis of the spectra takes into account that at the evaporation temperature of the metal at about 1800 K the fine structure states 3d(8) 4s(2) 3F and 3d(9) 4s 3D of both configurations 3d(8) 4s(2) and 3d(9) 4s are populated. The population of these two configurations offers the unique possibility for a comparison with the corresponding spectra in the condensed phase (Ni metal and NiO) where current configuration interaction calculations use the mixture of the configurations (3d,4s)(10). By using our theoretical description of the 2p photoionization new insight into these condensed phase spectra is found.