Prognostic significance of vascular endothelial growth factor expression in human ovarian carcinoma

The influence of vascular endothelial growth factor (VEGF) expression and microvessel density (MVD) on prognosis and the relationship between VEGF expression and MVD in ovarian carcinoma are not well defined. We studied VEGF expression in parallel with MVD by immunohistochemistry in 94 ovarian tumours (64 malignant, 13 borderline, and 17 benign) and correlated the results with the clinicopathologic prognostic factors of the disease to clarify their significance in this disease. Assessment of VEGF mRNA isoforms by RT-PCR was also performed. Of the malignant, borderline, and benign ovarian tumours respectively, two (3%), four (31%) and 16 (94%) were negative, 31 (48%), seven (54%) and one (6%) had low expressions, and 31 (48%), two (15%) and none (0%) had high expressions of VEGF. There were significant associations between the VEGF expression and disease stage (P = 0.002), histologic grade (P = 0.0004), and patient outcome (P = 0.0002). MVD did not correlate significantly with the clinicopathologic parameters. Likewise, no correlation was found between MVD and VEGF expression. The survival of patients with high VEGF expression was significantly worse than that of patients with low and negative VEGF expression (P = 0.0004). Multivariate analysis revealed that disease stage and VEGF expression were significant and independent prognostic indicators of overall survival time (P = 0.008 and P = 0.006 respectively). These findings suggest that in conjunction with the established clinicopathologic prognostic parameters of ovarian carcinoma, VEGF expression may enhance the predictability of patients at high risk for tumour progression who are potential candidates for further aggressive therapy. © 2000 Cancer Research Campaig

Anisotropic optical response of InP self-assembled quantum dots studied by pump-probe spectroscopy

Transient anisotropic reflectivity change spectra of InP quantum dots have been observed by means of two-color pump-probe spectroscopy. The results show a fast decay component with a lifetime of 100–200 ps which depends on the probe energy, followed by the slow decay component of ~1 ns. The reflectivity change spectra have a dispersive shape having a maximum on the higher energy side of the photoluminescence (PL) band by 80 meV, and a dip located at the maximum of the PL band. Interestingly, the reflectivity change signals observed for the [1[overline 1]0] and [110] polarizations have the opposite sign when the probe energy is set between the first and second exciton states. The temporal change of spectra is simulated by means of a Monte Carlo method, and the model is found to well reproduce the experimental result. Further, the model enables us to evaluate the microscopic exciton parameters of single quantum dots by macroscopic observations. The oscillator strengths along the [110] and [1[overline 1]0] directions at the PL peak energy are evaluated to be fx=0.37 and fy=0.71, respectively. The oscillator strength is about five times smaller than simple theoretical estimates. This suggests a small overlap of the envelope functions which is consistent with the existence of a permanent dipole moment observed in these QDs

Polarization-Correlated Photon Pairs from a Single Quantum Dot

Polarization correlation in a linear basis, but not entanglement, is observed between the biexciton and single-exciton photons emitted by a single InAs quantum dot in a two-photon cascade. The results are well described quantitatively by a probabilistic model that includes two decay paths for a biexciton through a non-degenerate pair of one-exciton states, with the polarization of the emitted photons depending on the decay path. The results show that spin non-degeneracy due to quantum-dot asymmetry is a significant obstacle to the realization of an entangled-photon generation device.Comment: 4 pages, 4 figures, revised discussio

Zero-field spin quantum beats in charged quantum dots

Spins of resident electrons in charged quantum dots (QD’s) act as local magnets inducing the Zeeman splitting of excitons trapped into dots. This is evidenced by the observation of quantum beats in the linearly polarized time-resolved photoluminescence of a biased array of self-assembled InP QD’s. An external magnetic field is found to shorten the spin beats’ decay time keeping constant the frequency of the beats. A model using the pseudospin formalism allows one to attribute the observed quantum beats to the radiative decay of hot trions having two electrons that occupy different energy levels in a QD

Sub-microsecond correlations in photoluminescence from InAs quantum dots

Photon correlation measurements reveal memory effects in the optical emission of single InAs quantum dots with timescales from 10 to 800 ns. With above-band optical excitation, a long-timescale negative correlation (antibunching) is observed, while with quasi-resonant excitation, a positive correlation (blinking) is observed. A simple model based on long-lived charged states is presented that approximately explains the observed behavior, providing insight into the excitation process. Such memory effects can limit the internal efficiency of light emitters based on single quantum dots, and could also be problematic for proposed quantum-computation schemes.Comment: 8 pages, 8 figure

Illuminating the reaction pathway of the FokI restriction endonuclease by fluorescence resonance energy transfer

The FokI restriction endonuclease is a monomeric protein that recognizes an asymmetric sequence and cleaves both DNA strands at fixed loci downstream of the site. Its single active site is positioned initially near the recognition sequence, distant from its downstream target 13 nucleotides away. Moreover, to cut both strands, it has to recruit a second monomer to give an assembly with two active sites. Here, the individual steps in the FokI reaction pathway were examined by fluorescence resonance energy transfer (FRET). To monitor DNA binding and domain motion, a fluorescence donor was attached to the DNA, either downstream or upstream of the recognition site, and an acceptor placed on the catalytic domain of the protein. A FokI variant incapable of dimerization was also employed, to disentangle the signal due to domain motion from that due to protein association. Dimerization was monitored separately by using two samples of FokI labelled with donor and acceptor, respectively. The stopped-flow studies revealed a complete reaction pathway for FokI, both the sequence of events and the kinetics of each individual step

Measurement and comparison of individual external doses of high-school students living in Japan, France, Poland and Belarus -- the "D-shuttle" project --

Twelve high schools in Japan (of which six are in Fukushima Prefecture), four in France, eight in Poland and two in Belarus cooperated in the measurement and comparison of individual external doses in 2014. In total 216 high-school students and teachers participated in the study. Each participant wore an electronic personal dosimeter "D-shuttle" for two weeks, and kept a journal of his/her whereabouts and activities. The distributions of annual external doses estimated for each region overlap with each other, demonstrating that the personal external individual doses in locations where residence is currently allowed in Fukushima Prefecture and in Belarus are well within the range of estimated annual doses due to the background radiation level of other regions/countries

DNA looping by FokI: the impact of synapse geometry on loop topology at varied site orientations

Most restriction endonucleases, including FokI, interact with two copies of their recognition sequence before cutting DNA. On DNA with two sites they act in cis looping out the intervening DNA. While many restriction enzymes operate symmetrically at palindromic sites, FokI acts asymmetrically at a non-palindromic site. The directionality of its sequence means that two FokI sites can be bridged in either parallel or anti-parallel alignments. Here we show by biochemical and single-molecule biophysical methods that FokI aligns two recognition sites on separate DNA molecules in parallel and that the parallel arrangement holds for sites in the same DNA regardless of whether they are in inverted or repeated orientations. The parallel arrangement dictates the topology of the loop trapped between sites in cis: the loop from inverted sites has a simple 180° bend, while that with repeated sites has a convoluted 360° turn. The ability of FokI to act at asymmetric sites thus enabled us to identify the synapse geometry for sites in trans and in cis, which in turn revealed the relationship between synapse geometry and loop topology