313 research outputs found
Time-resolved magnetic field effect on triplet formation in photosynthetic reaction centers of rhodopseudomonas sphaeroides R-26
Recombination dynamics in bacterial photosynthetic reaction centers
The time dependence of magnetic field effects on light absorption by triplet-state and radical ions in quinone-depleted reaction centers of Rhodopseudomonas sphaeroides strain R-26 has been investigated. Measurements on the time scale of the hyperfine interaction in the radical pair [(BChl)2+. ...BPh-.)] provided kinetic data characterizing the recombination process. The results have been interpreted in terms of a recently proposed model that assumes an intermediate electron acceptor (close site) between the bacteriochlorophyll "special pair" (BChl)2 and the bacteriopheophytin BPh (distant site). Recombination is assumed to proceed through this intermediate acceptor. The experiments led to effective recombination rates for the singlet and triplet channel: k(Seff) = 3.9 . 107 s-1 and k(Teff) = 7.4 . 10(8) s-1. These correspond to recombination rates ks = 1 . 10(1) s-1 and kT = 7.1 . 10(11) s-1 in the close configuration. The upper bound of the effective spin dephasing rate k2eff approximately equal to 1 . 10(9) s-1 is identical with the rate of the electron hopping between the distant site of zero spin exchange interaction and the close site of large interaction. Interpretation of data for the case of direct recombination yields the recombination rates, spin dephasing rate, and exchange interaction in a straightforward way
Antiferromagnetism at the YBa2Cu3O7 / La2/3Ca1/3MnO3 interface
The magnetic properties of a series of YBa2Cu3O7-x/La2/3Ca1/3MnO3
(YBCO/LC1/3MO) superlattices grown by dc sputtering at high oxygen pressures
(3.5 mbar) show the expected ferromagnetic behaviour. However, field cooled
hysteresis loops at low temperature show the unexpected existence of exchange
bias, effect associated with the existence of ferromagnetic/antiferromagnetic
(F/AF) interfaces. The blocking temperature (TB) is found thickness dependent
and the exchange bias field (HEB) is found inversely proportional to the FM
layer thickness, as expected. The presence of an AF material is probably
associated to interface disorder and Mn valence shift towards Mn4+.Comment: 12 pages, 2 figures, 1 table, submitted to Applied Physics Letter
Inhibition of fatty acid synthase sensitizes prostate cancer cells to radiotherapy
Many common human cancers, including colon, prostate and breast cancer, express high levels of fatty acid synthase compared to normal human tissues. This elevated expression is associated with protection against apoptosis, increased metastasis and poor prognosis. Inhibitors of fatty acid synthase, such as the cerulenin synthetic analog C75, decrease prostate cancer cell proliferation, increase apoptosis and decrease tumor growth in experimental models. Although radiotherapy is widely used in the treatment of prostate cancer patients, the risk of damage to neighboring normal organs limits the radiation dose that can be delivered. In this study, we examined the potential of fatty acid synthase inhibition to sensitize prostate cancer cells to radiotherapy. The efficacy of C75 alone or in combination with X irradiation was examined in monolayers and in multicellular tumor spheroids. Treatment with C75 alone decreased clonogenic survival, an effect that was abrogated by the antioxidant. C75 treatment also delayed spheroid growth in a concentration-dependent manner. The radiosensitizing effect of C75 was indicated by combination index values between 0.65 and 0.71 and the reduced surviving fraction of clonogens, in response to 2 Gy X irradiation, from 0.51 to 0.30 and 0.11 in the presence of 25 and 35 ÎŒM C75, respectively. This increased sensitivity to radiation was reduced by the presence of the antioxidant. The C75 treatment also enhanced the spheroid growth delay induced by X irradiation in a supra-additive manner. The level of radiation-induced apoptosis in prostate cancer cells was increased further by C75, which induced cell cycle arrest in the G2/M phase, but only at a concentration greater than that required for radiosensitization. Radiation-induced G2/M blockade was not affected by C75 treatment. These results suggest the potential use of fatty acid synthase inhibition to enhance the efficacy of radiotherapy of prostate carcinoma and that C75-dependent cell cycle arrest is not responsible for its radiosensitizing effect
Pitfalls in the synthesis of nanoscaled perovskite type compounds, Part I: influence of different sol-gel preparation methods and characterization of nanoscaled BaTiO3
Different solâgel routes are compared for the synthesis of nanoscaled BaTiO3 with respect to the reaction paths and the quality of the products. The various precursor systems differ largely in their behaviour during decomposition imposing quite different procedures for their thermal treatment. It is shown that the compositional homogeneity during the process of synthesis, which is the target of solâgel methods, may well be destroyed by the formation of intermediate compounds. It will only be restored after prolonged heating at higher temperatures where the crystallite sizes will in general have left the nanoregime. Due to such pitfalls the desired properties of the products with narrow size distributions will not always be ensured when working according to such recipes and the products obtained will behave quite differently in fabrication procedures like shaping and sintering of workpieces
Impurity band in clean superconducting weak links
Weak impurity scattering produces a narrow band with a finite density of
states near the phase difference in the mid-gap energy spectrum of
a macroscopic superconducting weak link. The equivalent distribution of
transmission coefficients of various cunducting quantum channels is found.Comment: 4 pages, 4 figures, changed conten
Policy Feedback and the Politics of the Affordable Care Act
There is a large body of literature devoted to how âpolicies create politicsâ and how feedback effects from existing policy legacies shape potential reforms in a particular area. Although much of this literature focuses on selfâreinforcing feedback effects that increase support for existing policies over time, Kent Weaver and his colleagues have recently drawn our attention to selfâundermining effects that can gradually weaken support for such policies. The following contribution explores both selfâreinforcing and selfâundermining policy feedback in relationship to the Affordable Care Act, the most important healthâcare reform enacted in the United States since the midâ1960s. More specifically, the paper draws on the concept of policy feedback to reflect on the political fate of the ACA since its adoption in 2010. We argue that, due in part to its sheer complexity and fragmentation, the ACA generates both selfâreinforcing and selfâundermining feedback effects that, depending of the aspect of the legislation at hand, can either facilitate or impede conservative retrenchment and restructuring. Simultaneously, through a discussion of partisan effects that shape Republican behavior in Congress, we acknowledge the limits of policy feedback in the explanation of policy stability and change
Black Titania and Niobia within Ten Minutes : Mechanochemical Reduction of Metal Oxides with Alkali Metal Hydrides
Partially or fully reduced transition metal oxides
show extraordinary electronic and catalytic properties but are
usually prepared by high temperature reduction reactions.
This study reports the systematic investigation of the fast
mechanochemical reduction of rutile-type TiO2 and H-Nb2O5
to their partially reduced black counterparts applying NaH
and LiH as reducing agents. Milling time and oxide to
reducing agent ratio show a large influence on the final
amount of reduced metal ions in the materials. For both
oxides LiH shows a higher reducing potential than NaH. An
intercalation of Li+ into the structure of the oxides was
proven by PXRD and subsequent Rietveld refinements as well
as 6
Li solid-state NMR spectroscopy. The products showed a
decreased band gap and the presence of unpaired electrons
as observed by EPR spectroscopy, proving the successful
reduction of Ti4+ and Nb5+. Furthermore, the developed
material exhibits a significantly enhanced photocatalytic
performance towards the degradation of methylene blue
compared to the pristine oxides. The presented method is a
general, time efficient and simple method to obtain reduced
transition metal oxides
Giant Josephson current through a single bound state in a superconducting tunnel junction
We study the microscopic structure of the Josephson current in a single-mode
tunnel junction with a wide quasiclassical tunnel barrier. In such a junction
each Andreev bound state carries a current of magnitude proportional to the
{\em amplitude} of the normal electron transmission through the junction.
Tremendous enhancement of the bound state current is caused by the resonance
coupling of superconducting bound states at both superconductor-insulator
interfaces of the junction. The possibility of experimental observation of the
single bound state current is discussed.Comment: 11 pages, [aps,preprint]{revtex
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