34 research outputs found
Direct observation of atomic diffusion in warm rubidium ensembles
We present a robust method for measuring the diffusion coefficients of warm
atoms in buffer gases. Using optical pumping, we manipulate the atomic spin in
a thin cylinder inside the cell. Then we observe the spatial spread of
optically pumped atoms in time using a camera, which allows us to determine the
diffusion coefficient. As an example, we demonstrate measurements of diffusion
coefficients of rubidium in neon, krypton and xenon acting as buffer gases. We
have determined the normalized (273 K, 760 Torr) diffusion coefficients to be
0.180.03 cm/s for neon, 0.070.01 cm/s for krypton, and
0.0520.006 cm/s for xenon.Comment: 6 pages, 5 figure
Respiratory dysfunction by AFG3L2 deficiency causes decreased mitochondrial calcium uptake via organellar network fragmentation
The mitochondrial protein AFG3L2 forms homo-oligomeric and hetero-oligomeric complexes with paraplegin in the inner mitochondrial membrane, named m-AAA proteases. These complexes are in charge of quality control of misfolded proteins and participate in the regulation of OPA1 proteolytic cleavage, required for mitochondrial fusion. Mutations in AFG3L2 cause spinocerebellar ataxia type 28 and a complex neurodegenerative syndrome of childhood. In this study, we demonstrated that the loss of AFG3L2 in mouse embryonic fibroblasts (MEFs) reduces mitochondrial Ca2+ uptake capacity. This defect is neither a consequence of global alteration in cellular Ca2+ homeostasis nor of the reduced driving force for Ca2+ internalization within mitochondria, since cytosolic Ca2+ transients and mitochondrial membrane potential remain unaffected. Moreover, experiments in permeabilized cells revealed unaltered mitochondrial Ca2+ uptake speed in Afg3l2â/â cells, indicating the presence of functional Ca2+ uptake machinery. Our results show that the defective Ca2+ handling in Afg3l2â/â cells is caused by fragmentation of the mitochondrial network, secondary to respiratory dysfunction and the consequent processing of OPA1. This leaves a number of mitochondria devoid of connections to the ER and thus without Ca2+ elevations, hampering the proper Ca2+ diffusion along the mitochondrial network. The recovery of mitochondrial fragmentation in Afg3l2â/â MEFs by overexpression of OPA1 rescues the impaired mitochondrial Ca2+ buffering, but fails to restore respiration. By linking mitochondrial morphology and Ca2+ homeostasis, these findings shed new light in the molecular mechanisms underlining neurodegeneration caused by AFG3L2 mutation
Inhibition of proteasome rescues a pathogenic variant of respiratory chain assembly factor COA7.
Nuclear and mitochondrial genome mutations lead to various mitochondrial diseases, many of which affect the mitochondrial respiratory chain. The proteome of the intermembrane space (IMS) of mitochondria consists of several important assembly factors that participate in the biogenesis of mitochondrial respiratory chain complexes. The present study comprehensively analyzed a recently identified IMS protein cytochrome c oxidase assembly factor 7 (COA7), or RESpiratory chain Assembly 1 (RESA1) factor that is associated with a rare form of mitochondrial leukoencephalopathy and complex IV deficiency. We found that COA7 requires the mitochondrial IMS import and assembly (MIA) pathway for efficient accumulation in the IMS We also found that pathogenic mutant versions of COA7 are imported slower than the wild-type protein, and mislocalized proteins are degraded in the cytosol by the proteasome. Interestingly, proteasome inhibition rescued both the mitochondrial localization of COA7 and complex IV activity in patient-derived fibroblasts. We propose proteasome inhibition as a novel therapeutic approach for a broad range of mitochondrial pathologies associated with the decreased levels of mitochondrial proteins.Narodowe Centrum Nauki (NCN) NCN 2012/05/B/NZ3/00781NCN 2015/19/B/NZ3/03272
Deutsche Forschungsgemeinschaft (DFG) SFB1190 (P13)
Fundacja na rzecz Nauki Polskiej (FNP) TEAM TECH CORE FACILITY/2016â2/2MAB/2017/2COP/01/2016
Ministerstwo Nauki i Szkolnictwa WyĆŒszego (MNiSW) Ideas Plus programme 000263
RCUK|Medical Research Council (MRC) MC_UU_00015/5
EC|FP7|FP7 Ideas: European Research Council (FP7 Ideas) FP7â322424339580
Institut de France
Telethon Italy GTB1200
A Comparison of 3D and 2D FE Frictional Heating Models for Long and Variable Applications of Railway Tread Brake
The article proposes two 3D and 2D numerical FE models of frictional heating for the estimation of temperature distributions in railway tread brake in 1xBg configuration during repeated long-term braking. The results of computations were compared with the time courses of temperature measured using thermocouples throughout the duration of the tests on a full-scale dynamometer for two different brake shoe materials in combination with a steel wheel. The resulting temperature distributions calculated using the proposed models agreed well with the experimental measurements, and the maximum difference in temperature values does not exceed 20%. It has been proven that 2D FE model can be as efficient as 3D model to estimate the temperature distribution during long-term and variable braking in the considered friction node. The differences in the calculation of the temperature values using these models did not exceed 3%, and the calculation time for the 2D model, compared to the 3D model, was shorter approximately 85 times for the braking cycle lasting 5032 s, and approximately 45 times for the braking cycle lasting 3297 s
Protein trafficking at the crossroads to mitochondria
AbstractMitochondria are central power stations in the cell, which additionally serve as metabolic hubs for a plethora of anabolic and catabolic processes. The sustained function of mitochondria requires the precisely controlled biogenesis and expression coordination of proteins that originate from the nuclear and mitochondrial genomes. Accuracy of targeting, transport and assembly of mitochondrial proteins is also needed to avoid deleterious effects on protein homeostasis in the cell. Checkpoints of mitochondrial protein transport can serve as signals that provide information about the functional status of the organelles. In this review, we summarize recent advances in our understanding of mitochondrial protein transport and discuss examples that involve communication with the nucleus and cytosol
Temporal imaging for ultra-narrowband few-photon states of light
Plenty of quantum information protocols are enabled by manipulation and
detection of photonic spectro-temporal degrees of freedom via light-matter
interfaces. While present implementations are well suited for high-bandwidth
photon sources such as quantum dots, they lack the high resolution required for
intrinsically narrow-band light-atom interactions. Here, we demonstrate
far-field temporal imaging based on ac-Stark spatial spin-wave phase
manipulation in a multimode gradient echo memory. We achieve spectral
resolution of 20 kHz with MHz-level bandwidth and ultra-low noise equivalent to
0.023 photons, enabling operation in the single-quantum regime.Comment: 10 pages, 9 figure
Massively-multiplexed generation of Bell-type entanglement using a quantum memory
High-rate generation of hybrid photon-matter entanglement remains a
fundamental building block of quantum network architectures enabling protocols
such as quantum secure communication or quantum distributed computing. While a
tremendous effort has been made to overcome technological constraints limiting
the efficiency and coherence times of current systems, an important
complementary approach is to employ parallel and multiplexed architectures.
Here we follow this approach experimentally demonstrating the generation of
bipartite polarization-entangled photonic states across more than 500 modes,
with a programmable delay for the second photon enabled by qubit storage in a
wavevector multiplexed cold-atomic quantum memory. We demonstrate Clauser,
Horne, Shimony, Holt inequality violation by over 3 standard deviations,
lasting for at least 45 {\mu}s storage time for half of the modes. The ability
to shape hybrid entanglement between the polarization and wavevector degrees of
freedom provides not only multiplexing capabilities but also brings prospects
for novel protocols