Blackbody-radiation-assisted molecular laser cooling

The translational motion of molecular ions can be effectively cooled sympathetically to temperatures below 100 mK in ion traps through Coulomb interactions with laser-cooled atomic ions. The distribution of internal rovibrational states, however, gets in thermal equilibrium with the typically much higher temperature of the environment within tens of seconds. We consider a concept for rotational cooling of such internally hot, but translationally cold heteronuclear diatomic molecular ions. The scheme relies on a combination of optical pumping from a few specific rotational levels into a ``dark state'' with redistribution of rotational populations mediated by blackbody radiation.Comment: 4 pages, 5 figure

Влияние фазового состава на физико-механические свойства композитов на основе нитридов кремния, бора и титана, спеченных под высоким давлением

Исследовано влияние фазового состава на физико–механические свойства композитов на основе нитридов кремния, бора и титана, с содержанием в исходной шихте субмикронного порошка BNсф в количестве 30 и 50 масс. % и нанопорошка BNсф – 50 масс. %., спеченных при давлении 5 ГПа и температурах 1200–1800 градусов С. Установлено, что температурный режим спекания, дисперсность порошка BNсф, степень окисления и фазовые превращения в нитридах бора и кремния оказывают определяющее влияние на уровень их свойств. Композиты с добавкой нанопорошка BNсф имеют наиболее высокие характеристики: твердость HKN – 27,6 ГПа, модуль Юнга – 534 ГПа, коэффициент Пуассона – 0,18.Досліджено вплив фазового складу на фізико-механічні властивості композитів на основі нітридів кремнію, бору та титану, з вмістом у вихідній шихті субмікронного порошку BNсф в кількості 30 і 50 мас.% і нанопорошків BNсф – 50 мас.%., що були спечені при тиску 5 ГПа і температурах 1200–1800 градусів С. Встановлено, що температурний режим спікання, дисперсність порошку BNсф, ступінь окислення і фазові перетворення в нітридах бору та кремнію мають визначальний вплив на рівень їх властивостей. Композити з добавкою нанопорошків BNсф мають найбільш високі характеристики: твердість HKN – 27,6 ГПа, модуль Юнга – 534 ГПа, коефіцієнт Пуассона – 0,18.The effect of the phase composition on the physico-mechanical properties of composites based on silicon nitrides, boron and titanium nitrides, with a content of submicron сBN powder in the initial charge of 30 and 50 wt. % and сBN nanopowder – 50 wt. % have been investigated. It was found that the temperature of sintering, the dispersion of the сBN powder, the degree of oxidation, and the phase transformations in boron and silicon nitrides exert a decisive influence on the level of their properties. Composites with cBN nanopowder additive have the highest characteristics: Knoop hardness is 27,6 GPa, Young's modulus is 534 GPa, Poisson's ratio is 0,18

Photoemission signature of momentum-dependent hybridization in CeCoIn5

Hybridization between f electrons and conduction bands (c-f hybridization) is a driving force for many unusual phenomena. To provide insight into it, systematic studies of CeCoIn 5 heavy fermion superconductor have been performed by angle-resolved photoemission spectroscopy (ARPES) in a large angular range at temperature of T = 6 K. The used photon energy of 122 eV corresponds to Ce 4d-4f resonance. Calculations carried out with the relativistic multiple scattering Korringa-Kohn-Rostoker method and one-step model of photoemission yielded realistic simulation of the ARPES spectra, indicating that Ce-In surface termination prevails. Surface states, which have been identified in the calculations, contribute significantly to the spectra. Effects of the hybridization strongly depend on wave vector. They include a dispersion of heavy electrons and bands gaining f-electron character when approaching Fermi energy. We have also observed a considerable variation of f-electron spectral weight at EF , which is normally determined by both matrix element effects and wave vector dependent c-f hybridization. Fermi surface scans covering a few Brillouin zones revealed large matrix element effects. A symmetrization of experimental Fermi surface, which reduces matrix element contribution, yielded a specific variation of 4f-electron enhanced spectral intensity at EF around Gamma barre and M barre points. Tight-binding approximation calculations for Ce-In plane provided the same universal distribution of 4f-electron density for a range of values of the parameters used in the model

Downregulation of Homologous Recombination DNA Repair Genes by HDAC Inhibition in Prostate Cancer Is Mediated through the E2F1 Transcription Factor

Histone deacetylase inhibitors (HDACis) re-express silenced tumor suppressor genes and are currently undergoing clinical trials. Although HDACis have been known to induce gene expression, an equal number of genes are downregulated upon HDAC inhibition. The mechanism behind this downregulation remains unclear. Here we provide evidence that several DNA repair genes are downregulated by HDAC inhibition and provide a mechanism involving the E2F1 transcription factor in the process.Applying Analysis of Functional Annotation (AFA) on microarray data of prostate cancer cells treated with HDACis, we found a number of genes of the DNA damage response and repair pathways are downregulated by HDACis. AFA revealed enrichment of homologous recombination (HR) DNA repair genes of the BRCA1 pathway, as well as genes regulated by the E2F1 transcription factor. Prostate cancer cells demonstrated a decreased DNA repair capacity and an increased sensitization to chemical- and radio-DNA damaging agents upon HDAC inhibition. Recruitment of key HR repair proteins to the site of DNA damage, as well as HR repair capacity was compromised upon HDACi treatment. Based on our AFA data, we hypothesized that the E2F transcription factors may play a role in the downregulation of key repair genes upon HDAC inhibition in prostate cancer cells. ChIP analysis and luciferase assays reveal that the downregulation of key repair genes is mediated through decreased recruitment of the E2F1 transcription factor and not through active repression by repressive E2Fs.Our study indicates that several genes in the DNA repair pathway are affected upon HDAC inhibition. Downregulation of the repair genes is on account of a decrease in amount and promoter recruitment of the E2F1 transcription factor. Since HDAC inhibition affects several pathways that could potentially have an impact on DNA repair, compromised DNA repair upon HDAC inhibition could also be attributed to several other pathways besides the ones investigated in this study. However, our study does provide insights into the mechanism that governs downregulation of HR DNA repair genes upon HDAC inhibition, which can lead to rationale usage of HDACis in the clinics

Electronic structure calculations on the C4 cluster

8 pages, 5 figures, 4 tables, 1 scheme.The ground and the electronically excited states of the C4 radical are studied using interaction configuration methods and large basis sets. Apart from the known isomers [l-C4(X ) and r-C4(X )], it is found that the ground singlet surface has two other stationary points: s-C4(X ) and d-C4(X ). The d-C4 form is the third isomer of this cluster. The isomerization pathways from one form to the other show that deep potential wells are separating each minimum. Multireference configuration interaction studies of the electronic excited states reveal a high density of electronic states of these species in the 0–2 eV energy ranges. The high rovibrational levels of l-C4() undergo predissociation processes via spin-orbit interactions with the neighboring state.This work has been supported by the Ministerio de Ciencia y Tecnología of Spain, Grant Nos. AYA2002-02117 and AYA2005-00702. Parts of this work have been done on the computers of CINECA (Bologna, Italy) and NERSC (UC Berkeley).Peer reviewe

The asymptotic region of the potential energy surfaces relevant for the O(P-3)+SO(X-3 Sigma(-)) reaction

International audienceThe potential energy surfaces (PESs) and the spin-orbit couplings for all states of sulfur dioxide correlating with the lowest O((3)p) + SO(X(3)Sigma(-)) asymptote have been calculated in the bond formation region employing correlated electronic wavefunctions. The PESs are found to be strongly anisotropic along the bending coordinate. For linear (OSO)-O-... approach, the Sigma states lie below the Pi states; for the (OOS)-O-... orientation the Pi/Sigma ordering is opposite. For perpendicular approaches their A' components form avoided crossings. The electron spin quantum number is no longer a good quantum number for geometries where the multiplets come close together. (c) 2005 Elsevier B.V. All rights reserved