Photoemission Spectroscopy Using Virtual Photons Emitted by Positron Sticking: A Complementary Probe for Top-Layer Surface Electronic Structures.

We present a spectroscopic method which utilizes virtual photons to selectively measure the electronic structure of the topmost atomic layer. These virtual photons are created when incident positrons transition from vacuum states to bound surface states on the sample surface and can transfer sufficient energy to excite electrons into the vacuum. The short interaction range of the virtual photons restricts the penetration depth to approximately the Thomas-Fermi screening length. Measurements and analysis of the kinetic energies of the emitted electrons made on a single layer of graphene deposited on Cu and on the clean Cu substrate show that the ejected electrons originate exclusively from the topmost atomic layer. Moreover, we find that the kinetic energies of the emitted electrons reflect the density of states at the surface. These results demonstrate that this technique will be a complementary tool to existing spectroscopic techniques in determining the electronic structure of 2D materials and fragile systems due to the absence of subsurface contributions and probe-induced surface damage.

Direct evidence for low-energy electron emission following O LVV Auger transitions at oxide surfaces.

Oxygen, the third most abundant element in the universe, plays a key role in the chemistry of condensed matter and biological systems. Here, we report evidence for a hitherto unexplored Auger transition in oxides, where a valence band electron fills a vacancy in the 2s state of oxygen, transferring sufficient energy to allow electron emission. We used a beam of positrons with kinetic energies of [Formula: see text] eV to create O 2s holes via matter-antimatter annihilation. This made possible the elimination of the large secondary electron background that has precluded definitive measurements of the low-energy electrons emitted through this process. Our experiments indicate that low-energy electron emission following the Auger decay of O 2s holes from adsorbed oxygen and oxide surfaces are very efficient. Specifically, our results indicate that the low energy electron emission following the Auger decay of O 2s hole is nearly as efficient as electron emission following the relaxation of O 1s holes in [Formula: see text]. This has important implications for the understanding of Auger-stimulated ion desorption, Coulombic decay, photodynamic cancer therapies, and may yield important insights into the radiation-induced reactive sites for corrosion and catalysis.

An optimized QF-binary expression system for use in zebrafish.

The zebrafish model organism has been of exceptional utility for the study of vertebrate development and disease through the application of tissue-specific labelling and overexpression of genes carrying patient-derived mutations. However, there remains a need for a binary expression system that is both non-toxic and not silenced over animal generations by DNA methylation. The Q binary expression system derived from the fungus Neurospora crassa is ideal, because the consensus binding site for the QF transcription factor lacks CpG dinucleotides, precluding silencing by CpG-meditated methylation. To optimize this system for zebrafish, we systematically tested several variants of the QF transcription factor: QF full length; QF2, which lacks the middle domain; QF2w, which is an attenuated version of QF2; and chimeric QFGal4. We found that full length QF and QF2 were strongly toxic to zebrafish embryos, QF2w was mildly toxic, and QFGal4 was well tolerated, when injected as RNA or expressed ubiquitously from stable transgenes. In addition, QFGal4 robustly activated a Tg(QUAS:GFPNLS) reporter transgene. To increase the utility of this system, we also modified the QF effector sequence termed QUAS, which consists of five copies of the QF binding site. Specifically, we decreased both the CpG dinucleotide content, as well as the repetitiveness of QUAS, to reduce the risk of transgene silencing via CpG methylation. Moreover, these modifications to QUAS removed leaky QF-independent neural expression that we detected in the original QUAS sequence. To demonstrate the utility of our QF optimizations, we show how the Q-system can be used for lineage tracing using a Cre-dependent Tg(ubi:QFGal4-switch) transgene. We also demonstrate that QFGal4 can be used in transient injections to tag and label endogenous genes by knocking in QFGal4 into sox2 and ubiquitin C genes.

Pulse length variation causing spectral distortions in OPO-based hyperspectral coherent Raman scattering microscopy.

Picosecond optical parametric oscillators (OPOs) with broad wavelength tunability are frequently used as light sources in hyperspectral coherent Raman scattering (CRS) microscopy. We investigate how changes in the pulse length during OPO wavelength tuning of the pump beam affect hyperspectral CRS imaging. We find that significant distortions of the resulting CRS spectra occur if the OPO is operated without monitoring pulse length variations. By utilizing a custom-written MATLAB based control program to counteract changes in pulse length, normalized and reproducible data sets can be acquired. We demonstrate this by comparing hyperspectral data obtained from pure substances, as well as relevant biological specimens.

Colonic diverticulitis in chemotherapy patients: should operative indications change? A retrospective cohort study.

INTRODUCTION: Management of the immunosuppressed patient with diverticular disease remains controversial. We report the largest series of colon cancer patients undergoing chemotherapy and hospitalized for acute diverticulitis, to determine whether recent treatment with systemic chemotherapy is associated with increased risk for/increased severity of recurrent diverticulitis. METHODS: Retrospective cohort study of adult patients hospitalized for an initial episode of acute colonic diverticulitis at Memorial Sloan Kettering Cancer Center, 1988-2004. Outcomes in patients receiving systemic chemotherapy within one month of admission for diverticulitis ("Chemo") were compared to outcomes of patients not receiving chemotherapy within the past month ("No-chemo"). RESULTS: A total 131 patients met inclusion criteria. Chemo patients did not differ significantly from No-chemo group in terms of severity of acute diverticulitis at index admission (13.2% vs. 4.4%, respectively, p = 0.12), resumption of chemotherapy (median 2 months), failure of non-operative management (13.2% vs 4.4%, respectively, p = 0.12), frequency of recurrence (20.5% vs 18.5%), hospital length of stay (p = 0.08), and likelihood of interval resection (24.0% vs. 16.2%, respectively, p = 0.39). Chemo patients recurred with more severe disease, were more likely to undergo emergent surgery (75.0% vs. 23.5%, respectively, p = 0.03), and were more likely to be diverted (100.0% vs. 25.0%, respectively, p = 0.03). Chemo patients were significantly more likely to incur a postoperative complication (100% vs 9.1% p < 0.01) following interval resection. Overall mortality was significantly higher in the Chemo vs. No-chemo group. Median survival in Chemo patients was 3.4 years; in No-chemo patients, median survival was not reached at 10 years. CONCLUSION: Our data do not support routine elective surgery for acute diverticulitis in patients receiving chemotherapy. Non-operative management in the acute or interval setting appears preferable whenever possible.

Luminescence of La0.2Y1.8O3 nanostructured scintillators.

For the first time, transparent La0.2Y1.8O3 nanostructured polycrystalline scintillators were fabricated by sintering nanoparticle powders at high temperatures and their scintillation properties are reported. La0.2Y1.8O3 is a host material that has never been investigated as scintillators for radiation detection. Our observations found that La0.2Y1.8O3 has an intense scintillation luminescence, a detection efficiency higher than that of YAG:Ce and a comparable energy resolution to NaI and CsI scintillators. In addition, La0.2Y1.8O3 is stable and has luminescence decay lifetime in the picosecond range which is favorable for radiation detection. The luminescence of La0.2Y1.8O3 has a large Stokes-shift and a large emission bandwidth, and the luminescence is highly temperature dependent. Different from most doped scintillators, the luminescence of La0.2Y1.8O3 is most likely from the self-trapped excitons. The discovery of La0.2Y1.8O3 scintillators opens a new door for the research of new materials for radiation detection.