High resolution X-ray spectra of the time evolution of emission from metastable electronic states of highly charged Ni-like ions.

Abstract: Metastable levels of highly charged ions that can only decay via highly forbidden transitions can have a significant effect on the properties of high temperature plasmas. For example, the highly forbidden 3d 10 J = 0 - 3d 9 4 s ( 5 2 , 1 2 ) J = 3 magnetic octupole (M3) transition in nickel-like ions can result in a large metastable population of its upper level which can then be ionized by electrons of energies below the ground state ionization potential. We present a method to study metastable electronic states in highly charged ions that decay by x-ray emission in electron beam ion traps (EBIT). The time evolution of the emission intensity can be used to study the parameters of ionization balance dynamics and the lifetime of metastable states. The temporal and energy resolution of a new transition-edge sensor microcalorimeter array enables these studies at the National Institute of Standards and Technology EBIT. Graphical abstract: NOMAD calculated time evolution of the ratio of the Ni-like and Co-like lines in Nd at varying electron densities compared with measured ratios.

Effect of artificial gravity on neurocognitive performance during head-down tilt bedrest.

This study evaluated the acute and chronic effects of intermittent and continuous Artificial Gravity (AG) on cognitive performance during 60 days of Head-down tilt bedrest (HDTBR), a well-established ground-based spaceflight analogue method. Participants were randomly assigned to three groups: intermittent AG, continuous AG, and HDTBR control group without AG exposure. Task performance and electrophysiological measures of attention and working memory were investigated during Simple and Complex tasks in the Visual and the Auditory modality. Compared to baseline, faster reaction time and better accuracy was present during HDTBR regarding the Complex tasks, however, the practice effect was diminished in the three HDTBR groups compared to an ambulatory control group. Brain potentials showed a modality-specific decrease, as P3a was decreased only in the Auditory, while P3b decreased in the Visual modality. No evidence for acute or chronic AG-related cognitive impairments during HDTBR was found.

Persistent deterioration of visuospatial performance in spaceflight.

Although human adaptation to spaceflight has been studied for decades, little is known about its long-term effects on brain and behavior. The present study investigated visuospatial performance and associated electrophysiological responses in astronauts before, during, and after an approximately half-year long mission to the International Space Station. Here we report findings demonstrating that cognitive performance can suffer marked decrements during spaceflight. Astronauts were slower and more error-prone on orbit than on Earth, while event-related brain potentials reflected diminished attentional resources. Our study is the first to provide evidence for impaired performance during both the initial (~ 8 days) and later (~ 50 days) stages of spaceflight, without any signs of adaptation. Results indicate restricted adaptability to spaceflight conditions and calls for new research prior to deep space explorations.

Changes in ionizing radiation dose rate affect cell cycle progression in adipose derived stem cells.

Biomedical use of radiation is utilized in effective diagnostic and treatment tools, yet can introduce risks to healthy tissues. High energy photons used for diagnostic purposes have high penetration depth and can discriminate multiple tissues based on attenuation properties of different materials. Likewise, the ability to deposit energy at various targets within tumors make the use of photons effective treatment for cancer. Radiation focused on a tumor will deposit energy when it interacts with a biological structure (e.g. DNA), which will result in cell kill should repair capacity of the tissue be overwhelmed. Likewise, damage to normal, non-cancerous tissues is a consequence of radiation that can lead to acute or late, chronic toxicity profiles. Adipose derived stem cells (ADSCs) are mesenchymal stem cells that have been proven to have similar characteristics to bone marrow derived stem cells, except that they are much easier to obtain. Within the body, ADSCs act as immunomodulators and assist with the maintenance and repair of tissues. They have been shown to have excellent differentiation capability, making them an extremely viable option for stem cell therapies and regenerative medicine applications. Due to the tissue ADSCs are derived from, they are highly likely to be affected by radiation therapy, especially when treating tumors localized to structures with relatively high ADSC content (eg., breast cancer). For this reason, the purpose behind this research is to better understand how ADSCs are affected by doses of radiation comparable to a single fraction of radiation therapy. We also measured the response of ADSCs to exposure at different dose rates to determine if there is a significant difference in the response of ADSCs to radiation therapy relevant doses of ionizing radiation. Our findings indicate that ADSCs exposed to Cesium (Cs 137)-gamma rays at a moderate dose of 2Gy and either a low dose rate (1.40Gy/min) or a high dose rate (7.31Gy/min) slow proliferation rate, and with cell cycle arrest in some populations. These responses ADSCs were not as marked as previously measured in other stem cell types. In addition, our results indicate that differences in dose rate in the Gy/min range typically utilized in small animal or cell irradiation platforms have a minimal effect on the function of ADSCs. The potential ADSCs have in the space of regenerative medicine makes them an ideal candidate for study with ionizing radiation, as they are one of the main cell types to promote tissue healing.

X-ray cabinet to deliver highly characterized low-dose soft x-ray radiation to biological samples.

We have designed, built, and tested a climate-controlled, radiation-shielded incubator cabinet for the purpose of analyzing the effects of low-dose x-ray radiation on biological tissues and cell cultures. Bremsstrahlung x rays incident on exchangeable fluorescence plates produce strong, quasi-monochromatic radiation directed toward a small container of biological samples. The x-ray source, sample, and detector are enclosed in an incubator-maintaining the optimal environment for biological samples to increase longevity to a maximum of 72 h. To demonstrate the capabilities of the setup, an example experiment is presented. Rat vascular smooth muscle cell growth was observed after irradiation with characteristic x rays of iron, copper, and calcium to impart doses of 2 mGy each. Cultures show significant spectrum dependent increases in cell number over controls at 48 h after irradiation. The experiment lends credence to the efficacy of the apparatus and shows promise for future low-dose bio-radiation studies.

Short-term cognitive fatigue effect on auditory temporal order judgments.

Fatigue is a core symptom in many psychological disorders and it can strongly influence everyday productivity. As fatigue effects have been typically demonstrated after long hours of time on task, it was surprising that in a previous study, we accidentally found a decline of temporal order judgment (TOJ) performance within 5-8 min. After replicating prior relevant findings we tested whether pauses and/or feedback relating the participant's performance to some "standard" can eliminate or reduce this short-term performance decline. We also assessed whether the performance decline is specific to the processes evoked by the TOJ task or it is a product of either general inattentiveness or the lack of willingness to thoroughly follow the task instructions. We found that both feedback and introducing pauses between successive measurements can largely reduce the performance decline, and that these two manipulations likely mobilize overlapping capacities. Performance decline was not present in a similar task when controlling for the TOJ threshold and it was not a result of uncooperative behavior. Therefore, we conclude that the TOJ threshold decline is either specific to temporal processing in general or to the TOJ task employed in the study. Overall, the results are compatible with the notion that the decline of TOJ threshold with repeated measures represents a short-term cognitive fatigue effect. This objective fatigue measure did not correlate with subjective fatigue. The latter was rather related to perceived difficulty/effort, the reduction of positive affectivity, heightened sensitivity to criticism, and the best TOJ threshold.

Differential impact of acute hypoxia on event related potentials: impaired task-irrelevant, but preserved task-relevant processing and response inhibition.

The current study investigated how experimentally induced acute normobaric hypoxia affects attentional control functions during easy, monotonous visual sustained attention and response inhibition (modified Continuous Performance Task) and executive control tasks (number-size Stroop task). Along with behavioral efficiency, task-relevant and task-irrelevant information processing were investigated by measuring event related brain potentials (ERP) evoked by target stimuli (Target P3), task-relevant stimuli with no response needed (NoGo P3), and task-irrelevant novel stimuli (Novelty P3) during acute hypoxia exposure. Normobaric hypoxia was induced by adjusting the O2 content of the breathing mixture to obtain 80% peripheral oxygen saturation, equivalent of 5500 m above sea level. Here we report decreased Novelty P3 during acute normobaric hypoxia exposure, while Target P3 and NoGo P3, as well as behavioral efficiency remained intact. Our paper is the first to provide evidence for impaired novelty processing along with intact task-relevant information processing and response inhibition during normobaric hypoxic exposure.

EBIT Observation of Ar Dielectronic Recombination Lines near the Unknown Faint X-Ray Feature Found in the Stacked Spectrum of Galaxy Clusters.

Motivated by possible atomic origins of the unidentified emission line detected at 3.55-3.57 keV in a stacked spectrum of galaxy clusters, an electron beam ion trap (EBIT) was used to investigate the resonant dielectronic recombination (DR) process in highly charged argon ions as a possible contributor to the emission feature. The He-like Ar DR-induced transition 1s22l-1s2l3l' was suggested to produce a 3.62 keV photon near the unidentified line at 3.57 keV and was the starting point of our investigation. The collisional-radiative model NOMAD was used to create synthetic spectra for comparison with both our EBIT measurements and with spectra produced with the AtomDB database/Astrophysical Plasma Emission Code (APEC) used in the Bulbul et al. work. Excellent agreement was found between the NOMAD and EBIT spectra, providing a high level of confidence in the atomic data used. Comparison of the NOMAD and APEC spectra revealed a number of missing features in the AtomDB database near the unidentified line. At an electron temperature of T e = 1.72 keV, the inclusion of the missing lines in AtomDB increases the total flux in the 3.5-3.66 keV energy band by a factor of 2. While important, this extra emission is not enough to explain the unidentified line found in the galaxy cluster spectra.

Cognitive resilience after prolonged task performance: an ERP investigation.

Deleterious consequences of cognitive fatigue might be avoided if people respond with increased effort to increased demands. In this study, we hypothesized that the effects of fatigue would be more pronounced in cognitive functions reflecting compensatory effort. Given that the P3a event-related potential is sensitive to the direction and amount of attention allocated to a stimulus array, we reasoned that compensatory effort would manifest in increased P3a amplitudes. Therefore, we compared P3a before (pre-test) and after (post-test) a 2 h long cognitively demanding (fatigue group, n = 18) or undemanding task (control group, n = 18). Two auditory tasks, a three-stimulus novelty oddball and a duration discrimination two-choice response task were presented to elicit P3a. In the fatigue group, we used the multi-attribute task battery as a fatigue-inducing task. This task draws on a broad array of attentional functions and imposed considerable workload. The control group watched mood-neutral documentary films. The fatigue manipulation was effective as subjective fatigue increased significantly in the fatigue group compared to controls. Contrary to expectations, however, fatigue failed to affect P3a in the post-test phase. Similar null effects were obtained for other neurobehavioral measures (P3b and behavioral performance). Results indicate that a moderate increase in subjective fatigue does not hinder cognitive functions profoundly. The lack of objective performance loss in the present study suggests that the cognitive system can be resilient against challenges instigated by demanding task performance.

Intensity modulated operating mode of the rotating gamma system.

PURPOSE: The purpose of this work was to explore two novel operation modalities of the rotating gamma systems (RGS) that could expand its clinical application to lesions in close proximity to critical organs at risk (OAR). METHODS: The approach taken in this study consists of two components. First, a Geant4-based Monte Carlo (MC) simulation toolkit is used to model the dosimetric properties of the RGS Vertex 360™ for the normal, intensity modulated radiosurgery (IMRS), and speed modulated radiosurgery (SMRS) operation modalities. Second, the RGS Vertex 360™ at the Rotating Gamma Institute in Debrecen, Hungary is used to collect experimental data for the normal and IMRS operation modes. An ion chamber is used to record measurements of the absolute dose. The dose profiles are measured using Gafchromic EBT3 films positioned within a spherical water equivalent phantom. RESULTS: A strong dosimetric agreement between the measured and simulated dose profiles and penumbra was found for both the normal and IMRS operation modes for all collimator sizes (4, 8, 14, and 18 mm diameter). The simulated falloff and maximum dose regions agree better with the experimental results for the 4 and 8 mm diameter collimators. Although the falloff regions align well in the 14 and 18 mm collimators, the maximum dose regions have a larger difference. For the IMRS operation mode, the simulated and experimental dose distributions are ellipsoidal, where the short axis aligns with the blocked angles. Similarly, the simulated dose distributions for the SMRS operation mode also adopt an ellipsoidal shape, where the short axis aligns with the angles where the orbital speed is highest. For both modalities, the dose distribution is highly constrained with a sharper penumbra along the short axes. CONCLUSIONS: Dose modulation of the RGS can be achieved with the IMRS and SMRS modes. By providing a highly constrained dose distribution with a sharp penumbra, both modes could be clinically applicable for the treatment of lesions in close proximity to critical OARs.

The effect of well-characterized, very low-dose x-ray radiation on fibroblasts.

The purpose of this study is to determine the effects of low-dose radiation on fibroblast cells irradiated by spectrally and dosimetrically well-characterized soft x-rays. To achieve this, a new cell culture x-ray irradiation system was designed. This system generates characteristic fluorescent x-rays to irradiate the cell culture with x-rays of well-defined energies and doses. 3T3 fibroblast cells were cultured in cups with Mylar® surfaces and were irradiated for one hour with characteristic iron (Fe) K x-ray radiation at a dose rate of approximately 550 µGy/hr. Cell proliferation, total protein analysis, flow cytometry, and cell staining were performed on fibroblast cells to determine the various effects caused by the radiation. Irradiated cells demonstrated increased proliferation and protein production compared to control samples. Flow cytometry revealed that a higher percentage of irradiated cells were in the G0/G1 phase of the cell cycle compared to control counterparts, which is consistent with other low-dose studies. Cell staining results suggest that irradiated cells maintained normal cell functions after radiation exposure, as there were no qualitative differences between the images of the control and irradiated samples. The result of this study suggest that low-dose soft x-ray radiation might cause an initial pause, followed by a significant increase, in proliferation. An initial "pause" in cell proliferation could be a protective mechanism of the cells to minimize DNA damage caused by radiation exposure. The new cell irradiation system developed here allows for unprecedented control over the properties of the x-rays given to the cell cultures. This will allow for further studies on various cell types with known spectral distribution and carefully measured doses of radiation, which may help to elucidate the mechanisms behind varied cell responses to low-dose x-rays reported in the literature.

Dissociated Components of Executive Control in Acute Hypobaric Hypoxia.

INTRODUCTION: The neurocognitive effects of acute hypobaric hypoxia are still largely unknown. This study was designed to test the hypothesis that executive control, an important component of cognition, is especially vulnerable to hypoxia. METHODS: Subjects participated in a simulated hypobaric chamber flight to 5500 m. Four auditory tasks were presented before, during, and after hypoxia: 1) Voice, and 2) Name variant of the Stroop task (both measuring conflict resolution); 3) go/no-go task (GNG; measuring inhibition); and 4) two-choice reaction time task (CRT; which is a noninhibitory control task). RESULTS: The Stroop effect increased during hypoxia: in the Voice Stroop it increased from 49.4 to 83.6 ms for reaction time and from 4.1 to 12.3% for accuracy; in the Name Stroop from 43.5 to 82.9 ms for reaction time (accuracy remained unchanged). Accuracy declined from 82.3 to 75.0% in CRT, and from 85.8 to 77.5% (averaged over stimulus types) in the GNG task. Importantly, accuracy decreased similarly to go and no-go stimuli in the GNG task, revealing unaffected inhibition. DISCUSSION: The findings suggest that tasks requiring conflict resolution are more likely to be impaired than tasks requiring inhibition of response. Furthermore, our results provide evidence for the distinct nature of inhibitory control functions.Takács E, Czigler I, Pató LG, Balázs L. Dissociated components of executive control in acute hypobaric hypoxia. Aerosp Med Hu Perform. 2017; 88(12):1081-1087.

Extreme Environment Effects on Cognitive Functions: A Longitudinal Study in High Altitude in Antarctica.

This paper focuses on the impact of long-term Antarctic conditions on cognitive processes. Behavioral responses and event-related potentials were recorded during an auditory distraction task and an attention network paradigm. Participants were members of the over-wintering crew at Concordia Antarctic Research Station. Due to the reduced partial pressure of oxygen this environment caused moderate hypoxia. Beyond the hypoxia, the fluctuation of sunshine duration, isolation and confinement were the main stress factors of this environment. We compared 6 measurement periods completed during the campaign. Behavioral responses and N1/MMN (mismatch negativity), N1, N2, P3, RON (reorientation negativity) event-related potential components have been analyzed. Reaction time decreased in both tasks in response to repeated testing during the course of mission. The alerting effect increased, the inhibition effect decreased and the orienting effect did not change in the ANT task. Contrary to our expectations the N2, P3, RON components related to the attentional functions did not show any significant changes. Changes attributable to early stages of information processing were observed in the ANT task (N1 component) but not in the distraction task (N1/MMN). The reaction time decrements and the N1 amplitude reduction in ANT task could be attributed to sustained effect of practice. We conclude that the Antarctic conditions had no negative impacts on cognitive activity despite the presence of numerous stressors.

Population based ranking of frameless CT-MRI registration methods.

BACKGROUND: Clinical practice often requires simultaneous information obtained by two different imaging modalities. Registration algorithms are commonly used for this purpose. Automated procedures are very helpful in cases when the same kind of registration has to be performed on images of a high number of subjects. Radiotherapists would prefer to use the best automated method to assist therapy planning, however there are not accepted procedures for ranking the different registration algorithms. PURPOSE: We were interested in developing a method to measure the population level performance of CT-MRI registration algorithms by a parameter of values in the [0,1] interval. MATERIALS AND METHODS: Pairs of CT and MRI images were collected from 1051 subjects. Results of an automated registration were corrected manually until a radiologist and a neurosurgeon expert both accepted the result as good. This way 1051 registered MRI images were produced by the same pair of experts to be used as gold standards for the evaluation of the performance of other registration algorithms. Pearson correlation coefficient, mutual information, normalized mutual information, Kullback-Leibler divergence, L1 norm and square L2 norm (dis)similarity measures were tested for sensitivity to indicate the extent of (dis)similarity of a pair of individual mismatched images. RESULTS: The square Hellinger distance proved suitable to grade the performance of registration algorithms at population level providing the developers with a valuable tool to rank algorithms. CONCLUSIONS: The developed procedure provides an objective method to find the registration algorithm performing the best on the population level out of newly constructed or available preselected ones.

Oblique effect in visual mismatch negativity.

We investigated whether visual orientation anisotropies (known as oblique effect) exist in non-attended visual changes using event-related potentials (ERP). We recorded visual mismatch negativity (vMMN) which signals violation of sequential regularities. In the visual periphery unattended, task-irrelevant Gábor patches were displayed in an oddball sequence while subjects performed a tracking task in the central field. A moderate change (50°) in the orientation of stimuli revealed no consistent change-related components. However, we found orientation-related differences around 170 ms in occipito-temporal areas in the amplitude of the ERPs evoked by standard stimuli. In a supplementary experiment we determined the amount of orientation difference that is needed for change detection in an active, attended paradigm. Results exhibited the classical oblique effect; subjects detected 10° deviations from cardinal directions, while threshold from oblique directions was 17°. These results provide evidence that perception of change could be accomplished at significantly smaller thresholds, than what elicits vMMN. In Experiment 2 we increased the orientation change to 90°. Deviant-minus-standard difference was negative in occipito-parietal areas, between 120 and 200 ms after stimulus onset. VMMNs to changes from cardinal angles were larger and more sustained than vMMNs evoked by changes from oblique angles. Changes from cardinal orientations represent a more detectable signal for the automatic change detection system than changes from oblique angles, thus increased vMMN to these "larger" deviances might be considered a variant of the magnitude of deviance effect rarely observed in vMMN studies.