We have investigated multiphoton multiple ionization dynamics of xenon atoms using a new x-ray free-electron laser facility, SPring-8 Angstrom Compact free electron LAser (SACLA) in Japan, and ...identified that Xe(n+) with n up to 26 is produced at a photon energy of 5.5 keV. The observed high charge states (n≥24) are produced via five-photon absorption, evidencing the occurrence of multiphoton absorption involving deep inner shells. A newly developed theoretical model, which shows good agreement with the experiment, elucidates the complex pathways of sequential electronic decay cascades accessible in heavy atoms. The present study of heavy-atom ionization dynamics in high-intensity hard-x-ray pulses makes a step forward towards molecular structure determination with x-ray free-electron lasers.
In high-intensity laser light, matter can be ionized by direct multiphoton absorption even at photon energies below the ionization threshold. However on tuning the laser to the lowest resonant ...transition, the system becomes multiply excited, and more efficient, indirect ionization pathways become operative. These mechanisms are known as interatomic Coulombic decay (ICD), where one of the species de-excites to its ground state, transferring its energy to ionize another excited species. Here we show that on tuning to a higher resonant transition, a previously unknown type of interatomic Coulombic decay, intra-Rydberg ICD occurs. In it, de-excitation of an atom to a close-lying Rydberg state leads to electron emission from another neighbouring Rydberg atom. Moreover, systems multiply excited to higher Rydberg states will decay by a cascade of such processes, producing even more ions. The intra-Rydberg ICD and cascades are expected to be ubiquitous in weakly-bound systems exposed to high-intensity resonant radiation.
Inner-shell ionization of an isolated atom typically leads to Auger decay. In an environment, for example, a liquid or a van der Waals bonded system, this process will be modified, and becomes part ...of a complex cascade of relaxation steps. Understanding these steps is important, as they determine the production of slow electrons and singly charged radicals, the most abundant products in radiation chemistry. In this communication, we present experimental evidence for a so-far unobserved, but potentially very important step in such relaxation cascades: Multiply charged ionic states after Auger decay may partially be neutralized by electron transfer, simultaneously evoking the creation of a low-energy free electron (electron transfer-mediated decay). This process is effective even after Auger decay into the dicationic ground state. In our experiment, we observe the decay of Ne
produced after Ne 1s photoionization in Ne-Kr mixed clusters.
Glioblastomas (GBMs) are the most common and aggressive type of brain tumor. GBMs usually show hyperactivation of the PI3K-Akt pathway, a pro-tumorigenic signaling cascade that contributes to ...pathogenesis. Girdin, an actin-binding protein identified as a novel substrate of Akt, regulates the sprouting of axons and the migration of neural progenitor cells during early postnatal-stage neurogenesis in the hippocampus. Here, we show that Girdin is highly expressed in human glioblastoma (GBM). Stable Girdin knockdown in isolated GBM stem cells resulted in decreased expression of stem cell markers, including CD133, induced multilineage neural differentiation, and inhibited in vitro cell motility, ex vivo invasion, sphere-forming capacity and in vivo tumor formation. Furthermore, exogenous expression of the Akt-binding domain of Girdin, which competitively inhibits its Akt-mediated phosphorylation, diminished the expression of stem cell markers, SOX2 and nestin, and migration on the brain slice and induced the expression of neural differentiation markers glial fibrillary acidic protein/βIII Tubulin. Our results reveal that Girdin is required for GBM-initiating stem cells to sustain the stemness and invasive properties.
Background
The aim of this study was to evaluate whether MRI at 3 T with superparamagnetic iron oxide (SPIO) enhancement is an accurate and useful method for detecting metastases in sentinel nodes ...identified by CT‐lymphography (CT‐LG) in patients with breast cancer. The results were compared with those obtained using CT‐LG alone and diagnosing metastasis according to size criteria.
Methods
Patients with clinically node‐negative breast cancer were included. Sentinel nodes identified by CT‐LG were evaluated prospectively using SPIO‐enhanced MRI at 3 T. Sentinel node size was measured on CT‐LG, and a node larger than 5 mm in short‐axis diameter was considered metastatic. Sentinel nodes localized by CT‐LG were removed, and imaging results and histopathological findings were compared.
Results
Sentinel nodes were identified successfully by CT‐LG in 69 (99 per cent) of 70 patients. All 19 patients with a finding of metastasis in sentinel nodes at pathology were also shown to have metastases on MRI. Forty‐eight of 50 patients with non‐metastatic sentinel nodes diagnosed at pathology were classified as having non‐metastatic nodes on MRI. On a patient‐by‐patient basis, the sensitivity, specificity and accuracy of MRI for the diagnosis of sentinel node metastases were 100, 96 and 97 per cent; respective values for CT‐LG were 79, 56 and 62 per cent. The specificity and accuracy of MRI were superior to those of CT‐LG (P < 0·001 and P = 0·002 respectively).
Conclusion
SPIO‐enhanced MRI at 3 T is useful for accurate diagnosis of metastatic sentinel nodes, indicating that sentinel node biopsy may be avoided in patients with breast cancer who have non‐metastatic sentinel nodes on imaging.
Imaging replaces sentinel node biopsy
X-ray free-electron lasers have, over the past decade, opened up the possibility of understanding the ultrafast response of matter to intense X-ray pulses. In earlier research on atoms and small ...molecules, new aspects of this response were uncovered, such as rapid sequences of inner-shell photoionization and Auger ionization. Here, we studied a larger molecule, buckminsterfullerene (C60), exposed to 640 eV X-rays, and examined the role of chemical effects, such as chemical bonds and charge transfer, on the fragmentation following multiple ionization of the molecule. To provide time resolution, we performed femtosecond-resolved X-ray pump/X-ray probe measurements, which were accompanied by advanced simulations. The simulations and experiment reveal that despite substantial ionization induced by the ultrashort (20 fs) X-ray pump pulse, the fragmentation of C60 is considerably delayed. This work uncovers the persistence of the molecular structure of C60, which hinders fragmentation over a timescale of hundreds of femtoseconds. Furthermore, we demonstrate that a substantial fraction of the ejected fragments are neutral carbon atoms. These findings provide insights into X-ray free-electron laser-induced radiation damage in large molecules, including biomolecules.
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