2,765 research outputs found
Energetics of the primary electron transfer reaction revealed by ultrafast spectroscopy on modified bacterial reaction centers
The modification of reaction centers from Rhodobacter sphaeroides by the introduction of pheophytins instead of bacteriopheophytins leads to interesting changes in the primary photosynthetic reaction: long-living populations of the excited electronic state of the special pair P* and the bacteriochlorophyll anion B−A show up. The data allow the determination of the energetics in the reaction center. The free energy of the first intermediate P+B−A, where the electron has reached the accessory bacteriochlorophyll BA lies ≈ 450 cm−1 below the initially excited special pair P*
The Geography of Sexual Orientation: Structural Stigma and Sexual Attraction, Behavior, and Identity Among Men Who Have Sex with Men Across 38 European Countries.
: While the prevalence of sexual identities and behaviors of men who have sex with men (MSM) varies across countries, no study has examined country-level structural stigma toward sexual minorities as a correlate of this variation. Drawing on emerging support for the context-dependent nature of MSM's open sexual self-identification cross-nationally, we examined country-level structural stigma as a key correlate of the geographic variation in MSM's sexual attraction, behavior, and identity, and concordance across these factors. Data come from the European MSM Internet Survey, a multi-national dataset containing a multi-component assessment of sexual orientation administered across 38 European countries (NÂ =Â 174,209). Country-level stigma was assessed using a combination of national laws and policies affecting sexual minorities and a measure of attitudes toward sexual minorities held by the citizens of each country. Results demonstrate that in more stigmatizing countries, MSM were significantly more likely to report bisexual/heterosexual attractions, behaviors, and identities, and significantly less likely to report concordance across these factors, than in less stigmatizing countries. Settlement size moderated associations between country-level structural stigma and odds of bisexual/heterosexual attraction and behavior, such that MSM living in sparsely populated locales within high-structural stigma countries were the most likely to report bisexual or heterosexual behaviors and attractions. While previous research has demonstrated associations between structural stigma and adverse physical and mental health outcomes among sexual minorities, this study was the first to show that structural stigma was also a key correlate not only of sexual orientation identification, but also of MSM's sexual behavior and even attraction. Findings have implications for understanding the ontology of MSM's sexuality and suggest that a comprehensive picture of MSM's sexuality will come from attending to the local contexts surrounding this important segment of the global population.<br/
Detection of Cellular Senescence Reveals the Existence of Senescent Tumor Cells within Invasive Breast Carcinomas and Related Metastases
Oncogene-induced senescence is thought to constitute a barrier to carcinogenesis by arresting cells at risk of malignant transformation. However, numerous findings suggest that senescent cells may conversely promote tumor growth and metastatic progression, for example, through the senescence-associated secretory phenotype (SASP) they produce. Here, we investigated the degree to which senescent tumor cells exist within untreated human primary breast carcinomas and whether the presence of senescent cancer cells in primary tumors is recapitulated in their matched lymph node metastases. For the detection of senescence, we used SA-β-galactosidase (SA-β-gal) staining and other senescence markers such as Ki67, p21, p53, and p16. In patients with invasive luminal A and B breast carcinomas, we found broad similarities in the appearance of cancer cells between primary tumors and their corresponding metastases. Analysis of lymph nodes from patients with other breast cancer subtypes also revealed senescent tumor cells within metastatic lesions. Collectively, our findings show that senescent tumor cells exist within primary breast carcinomas and metastatic lesions. These results suggest a potential role for senescent breast tumor cells during metastatic progression and raise the question as to whether the targeting of senescent tumor cells with anti-senescent drugs might represent a novel avenue for improved treatment of breast and other cancers
Functional characterization of circulating tumor cells (CTCs) from metastatic ER+/HER2− breast cancer reveals dependence on HER2 and FOXM1 for endocrine therapy resistance and tumor cell survival: Implications for treatment of ER+/HER2− breast cancer
Mechanisms of acquired endocrine resistance and late recurrence in patients with ER+/HER2− breast cancer are complex and not fully understood. Here, we evaluated mechanisms of acquired resistance in circulating tumor cells (CTCs) from an ER+/HER2− breast cancer patient who initially responded but later progressed under endocrine treatment. We found a switch from ERα-dependent to HER2-dependent and ERα-independent expression of FOXM1, which may enable disseminated ER+/HER2− cells to re-initiate tumor cell growth and metastasis formation in the presence of endocrine treatment. Our results also suggest a role for HER2 in resistance, even in ER+ breast cancer cells that have neither HER2 amplification nor activating HER2 mutations. We found that NFkB signaling sustains HER2 and FOXM1 expression in CTCs in the presence of ERα inhibitors. Inhibition of NFkB signaling blocked expression of HER2 and FOXM1 in the CTCs, and induced apoptosis. Thus, targeting of NFkB and FOXM1 might be an efficient therapeutic approach to prevent late recurrence and to treat endocrine resistance. Collectively our data show that CTCs from patients with endocrine resistance allow mechanisms of acquired endocrine resistance to be delineated, and can be used to test potential drug regimens for combatting resistance
Effect of confinement potential shape on exchange interaction in coupled quantum dots
Exchange interaction has been studied for electrons in coupled quantum dots
(QD's) by a configuration interaction method using confinement potentials with
different profiles. The confinement potential has been parametrized by a
two-centre power-exponential function, which allows us to investigate various
types of QD's described by either soft or hard potentials of different range.
For the soft (Gaussian) confinement potential the exchange energy decreases
with increasing interdot distance due to the decreasing interdot tunnelling.
For the hard (rectangular-like) confinement potential we have found a
non-monotonic behaviour of the exchange interaction as a function of distance
between the confinement potential centres. In this case, the exchange
interaction energy exhibits a pronounced maximum for the confinement potential
profile which corresponds to the nanostructure composed of the small inner QD
with a deep potential well embedded in the large outer QD with a shallow
potential well. This effect results from the strong localization of electrons
in the inner QD, which leads to the large singlet-triplet splitting.
Implications of this finding for quantum logic operations have been discussed.Comment: 16 pages, including 11 figure
Time-resolved spectroscopy of the primary photosynthetic processes of membrane-bound reaction centers from an antenna-deficient mutant of Rhodobacter capsulatus
The primary photosynthetic reactions in whole membranes of the antenna-deficient mutant strain U43 (pTXA6–10) of Rhodobacter capsulatus are studied by transient absorption and emission spectroscopy with subpicosecond time resolution. Extensive similarities between the transient absorption data on whole membranes and on isolated reaction centers support the idea that the primary processes in isolated reaction centers are not modified by the isolation procedure
Detailed studies of the subpicosecond kinetics in the primary electron transfer of reaction centers of Rhodopseudomonas viridis
The primary, light-induced charge separation in reaction centers of Rhodopseudomonas viridis is investigated with femtosecond time resolution. The absorption changes after direct excitation of the primary donor P at 955 nm are investigated in the time range from 100 fs to 600 ps. The experimental data, taken at various probing wavelengths, reveal one subpicosecond and two picosecond time constants: 0.65 ± 0.2 ps, 3.5 ± 0.4 ps, and 200 ± 20 ps. The previously undetected 0.65 ps kinetics can be observed clearly in the spectral range of the Qx and Qy transitions of the monomeric bacteriochlorophylls. The experimental data support the idea that the accessory bacteriochlorophyll B A participates in the electron-transfer process.
Reference
Multiple low-temperature skyrmionic states in a bulk chiral magnet
Magnetic skyrmions are topologically protected nanoscale spin textures with particle-like properties. In bulk cubic helimagnets, they appear under applied magnetic fields and condense spontaneously into a lattice in a narrow region of the phase diagram just below the magnetic ordering temperature, the so-called A-phase. Theory, however, predicts skyrmions to be locally stable in a wide range of magnetic fields and temperatures. Our neutron diffraction measurements reveal the formation of skyrmion states in large areas of the magnetic phase diagram, from the lowest temperatures up to the A-phase. We show that nascent and disappearing spiral states near critical lines catalyze topological charge changing processes, leading to the formation and destruction of skyrmionic states at low temperatures, which are thermodynamically stable or metastable depending on the orientation and strength of the magnetic field. Skyrmions are surprisingly resilient to high magnetic fields: the memory of skyrmion lattice states persists in the field polarized state, even when the skyrmion lattice signal has disappeared. These findings highlight the paramount role of magnetic anisotropies in stabilizing skyrmionic states and open up new routes for manipulating these quasi-particles towards energy-efficient spintronics applications
Near-adiabatic parameter changes in correlated systems: Influence of the ramp protocol on the excitation energy
We study the excitation energy for slow changes of the hopping parameter in
the Falicov-Kimball model with nonequilibrium dynamical mean-field theory. The
excitation energy vanishes algebraically for long ramp times with an exponent
that depends on whether the ramp takes place within the metallic phase, within
the insulating phase, or across the Mott transition line. For ramps within
metallic or insulating phase the exponents are in agreement with a perturbative
analysis for small ramps. The perturbative expression quite generally shows
that the exponent depends explicitly on the spectrum of the system in the
initial state and on the smoothness of the ramp protocol. This explains the
qualitatively different behavior of gapless (e.g., metallic) and gapped (e.g.,
Mott insulating) systems. For gapped systems the asymptotic behavior of the
excitation energy depends only on the ramp protocol and its decay becomes
faster for smoother ramps. For gapless systems and sufficiently smooth ramps
the asymptotics are ramp-independent and depend only on the intrinsic spectrum
of the system. However, the intrinsic behavior is unobservable if the ramp is
not smooth enough. This is relevant for ramps to small interaction in the
fermionic Hubbard model, where the intrinsic cubic fall-off of the excitation
energy cannot be observed for a linear ramp due to its kinks at the beginning
and the end.Comment: 24 pages, 6 figure
Scale-invariant magnetic anisotropy in RuCl at high magnetic fields
In RuCl, inelastic neutron scattering and Raman spectroscopy reveal a
continuum of non-spin-wave excitations that persists to high temperature,
suggesting the presence of a spin liquid state on a honeycomb lattice. In the
context of the Kitaev model, magnetic fields introduce finite interactions
between the elementary excitations, and thus the effects of high magnetic
fields - comparable to the spin exchange energy scale - must be explored. Here
we report measurements of the magnetotropic coefficient - the second derivative
of the free energy with respect to magnetic field orientation - over a wide
range of magnetic fields and temperatures. We find that magnetic field and
temperature compete to determine the magnetic response in a way that is
independent of the large intrinsic exchange interaction energy. This emergent
scale-invariant magnetic anisotropy provides evidence for a high degree of
exchange frustration that favors the formation of a spin liquid state in
RuCl.Comment: arXiv admin note: substantial text overlap with arXiv:1901.09245.
Nature Physic
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