Room-temperature tunnel current amplifier and experimental setup for high resolution electronic spectroscopy in millikelvin STM experiments

The spectroscopic resolution of tunneling measurements performed with a scanning tunneling microscope is ultimately limited by the temperature at which the experiment is performed. To take advantage of the potential high spectroscopic resolution associated with operating an STM in a dilution refrigerator we have designed a room temperature tunnel current amplifier having very small back-action on the tunnel contact and allowing to nearly reach the predicted energy resolution. This design is a modification of the standard op-amp based tip-biasing current-voltage converter which implements differential voltage sensing and whose back action on the tip voltage is only ~2 $\mu$V rms for a 14 MV/A transimpedance and 22 kHz bandwidth.Comment: Available at http://www-spht.cea.fr/articles/s06/03

GCIRS 7, a pulsating M1 supergiant at the Galactic centre. Physical properties and age

The stellar population in the central parsec of the Galaxy is dominated by an old (several Gyr) population, but young, massive stars dominate the luminosity function. We have studied the most luminous of these stars, GCIRS 7, in order to constrain the age of the recent star formation event in the Galactic Centre and to characterise it as an interferometric reference for observations of the Galactic Centre with the instrument GRAVITY, which will equip the Very Large Telescope Interferometer in the near future. We present the first H-band interferometric observations of GCIRS 7, obtained using the PIONIER visitor instrument on the VLTI using the four 8.2-m unit telescopes. In addition, we present unpublished K-band VLTI/AMBER data, build JHKL light-curves based on data spanning 4 decades, and measured the star's effective temperature using SINFONI spectroscopy. GCIRS 7 is marginally resolved at H-band (in 2013: uniform-disk diameter=1.076+/-0.093mas, R=960+/-92Rsun at 8.33+/-0.35kpc). We detect a significant circumstellar contribution at K-band. The star and its environment are variable in brightness and in size. The photospheric H-band variations are well modelled with two periods: P0~470+/-10 days (amplitude ~0.64mag) and long secondary period LSP~2700-2850 days (~1.1mag). As measured from CO equivalent width, =3600+/-195K. The size, periods, luminosity (=-8.44+/-0.22) and effective temperature are consistent with an M1 supergiant with an initial mass of 22.5+/-2.5Msun and an age of 6.5-10Myr (depending on rotation). This age is in remarkable agreement with most estimates for the recent star formation event in the central parsec. Caution should be taken when using this star as an interferometric reference as it is variable in size, is surrounded by a variable circumstellar environment and large convection cells may form on its photosphere.Comment: Accepted for publication in A&A. 10 pages, 12 figure

Reaction, Levy Flights, and Quenched Disorder

We consider the A + A --> emptyset reaction, where the transport of the particles is given by Levy flights in a quenched random potential. With a common literature model of the disorder, the random potential can only increase the rate of reaction. With a model of the disorder that obeys detailed balance, however, the rate of reaction initially increases and then decreases as a function of the disorder strength. The physical behavior obtained with this second model is in accord with that for reactive turbulent flow, indicating that Levy flight statistics can model aspects of turbulent fluid transport.Comment: 6 pages, 5 pages. Phys. Rev. E. 65 (2002) 011109--1-

Thermal Properties of Heavy Fermion Compound YbP

Low-temperature specific heat and its field-dependence up to 16 T was measured in a stoichiometric single crystal of YbP. A sharp peak was observed at {\it T}$_{\rm N}$ = 0.53 K in zero magnetic field. Application of external field seems to induce a new magnetic phase above 11 T. The field dependence of the transition temperature in the high-field phase is different from that of the low field phase. The linear coefficient of the electronic specific heat is estimated as 120 mJ/mole K$^{2}$ from low temperature specfic heat, suggesting heavy Fermion state in YbP.Comment: to be published in J.Phys.Soc.Jpn on May, 200

Deformation of the N=Z nucleus 76Sr using beta-decay studies

A novel method of deducing the deformation of the N=Z nucleus 76Sr is presented. It is based on the comparison of the experimental Gamow-Teller strength distribution B(GT) from its beta decay with the results of QRPA calculations. This method confirms previous indications of the strong prolate deformation of this nucleus in a totally independent way. The measurement has been carried out with a large Total Absorption gamma Spectrometer, "Lucrecia", newly installed at CERN-ISOLDE.Comment: Accepted in Phys. Rev. Letter

An ISOCAM survey through gravitationally lensing galaxy clusters

ISOCAM was used to perform a deep survey through three gravitationally lensing clusters of galaxies. Nearly seventy sq. arcmin were covered over the clusters A370, A2218 and A2390. We present maps and photometry at 6.7 & 14.3 microns, showing a total of 145 mid-IR sources and the associated source counts. The 15 micron counts reach the faintest level yet recorded. All sources have counterparts in the optical or near-IR. Models of the clusters were used to correct for the effects of lensing, which increases the sensitivity of the survey. Seven of fifteen SCUBA sources were detected at 15 microns. Five have redshift between 0.23 & 2.8, with a median of 0.9. The field sources were counted to a lensing-corrected sensitivity of 30 microJy at 15 microns, and 14 microJy at 7 microns. The counts, corrected for completeness, contamination by cluster sources and lensing, confirm and extend findings of an excess by a factor of ten in the 15 micron population with respect to source models with no evolution. Source redshifts are mostly between 0.4 and 1.5. For the counts at 7 microns, integrating from 14 microJy to 460 microJy, we resolve 0.49+/-0.2 nW.m^(-2).sr^(-1) of the infrared background light (IBL) into discrete sources. At 15 microns we include the counts from other ISOCAM surveys to integrate from 30 microJy to 50 mJy, two to three times deeper than unlensed surveys, to resolve 2.7+/-0.62 nW.m^(-2).sr^(-1) of the IBL. These values are 10% and 55%, respectively, of the upper limit to the IBL, derived from photon-photon pair production of the TeV gamma rays from BL-Lac sources on the IBL photons. However, recent detections of TeV gamma rays from the z=0.129 BL Lac H1426+428 suggest that the 15 micron background reported implies substantial absorption of TeV photons from that source.Comment: 35 pages, 17 figures, to appear in Astronomy and Astrophysics, full paper with high-resolution figures available at http://www.iso.vilspa.esa.es/science/pub/2003

Chemical genetics analysis of an aniline mustard anticancer agent reveals complex I of the electron transport chain as a target

Supplementary information is available at the Journal of Biological Chemistry website.The antitumor agent 11β (CAS 865070-37-7), consisting of a DNA-damaging aniline mustard linked to an androgen receptor (AR) ligand, is known to form covalent DNA adducts and to induce apoptosis potently in AR-positive prostate cancer cells in vitro; it also strongly prevents growth of LNCaP xenografts in mice. The present study describes the unexpectedly strong activity of 11β against the AR-negative HeLa cells, both in cell culture and tumor xenografts, and uncovers a new mechanism of action that likely explains this activity. Cellular fractionation experiments indicated that mitochondria are the major intracellular sink for 11β; flow cytometry studies showed that 11β exposure rapidly induced oxidative stress, mitochondria being an important source of reactive oxygen species (ROS). Additionally, 11β inhibited oxygen consumption both in intact HeLa cells and in isolated mitochondria. Specifically, 11β blocked uncoupled oxygen consumption when mitochondria were incubated with complex I substrates, but it had no effect on oxygen consumption driven by substrates acting downstream of complex I in the mitochondrial electron transport chain. Moreover, 11β enhanced ROS generation in isolated mitochondria, suggesting that complex I inhibition is responsible for ROS production. At the cellular level, the presence of antioxidants (N-acetylcysteine or vitamin E) significantly reduced the toxicity of 11β, implicating ROS production as an important contributor to cytotoxicity. Collectively, our findings establish complex I inhibition and ROS generation as a new mechanism of action for 11β, which supplements conventional DNA adduct formation to promote cancer cell death.National Institutes of Health (U.S.) (Grant R01 CA077743)United States. Dept. of Defense (Prostate Cancer Research Program Award DAMD17-98-1-8520

PD-L1 Expression in Endometrial Carcinoma Cells and Intratumoral Immune Cells Differences Across Histologic and TCGA-based Molecular Subgroups

Programmed death-ligand 1 (PD-L1) is a biomarker that may predict the response to anti-programmed death 1/PD-L1 immunotherapy. We evaluated the expression of PD-L1 in carcinoma cells (Ca) and immune cells (ICs) across histopathologic and The Cancer Genome Atlas (TCGA) molecular subgroups of endometrial carcinoma (EC). Our study included 842 patients with EC. Direct sequencing of polymerase epsilon (POLE) exonuclease domain hot spots and conventional immunohistochemistry (MLH1, PMS2, MSH2, MSH6, p53) were conducted to identify TCGA classification-based molecular subgroups of EC: POLE-mutated, mismatch repair deficient, no specific molecular profile, and p53 aberrant. Multiplex immunohistochemistry was performed to evaluate PD-L1 expression in Ca and tumor-infiltrating ICs. PD-L1 expression in Ca and in ICs was detected in 8.6% and 27.7% of the cases, respectively. A combined positive score (CPS) was >= 1% in 19.4% of the samples. PD-L1 positivity in Ca and ICs, and CPS correlated with tumor T-cell density (P= 1% (P=0.037) positivity compared with early disease. In conclusion, PD-L1 expression profiles differ between molecular subclasses, histologic subtypes, and disease stage of EC. Prospective studies are needed to explore the predictive value of various PD-L1 scoring systems within the subgroups of EC. CPS presents methodological advantages over cell type-specific scoring systems.Peer reviewe