673 research outputs found
Purification of the head-pieces of the elementary particles from beef heart mitochondria: their morphological structure and enzymatic activity
1. In order to obtain direct evidence for the enzymatic identification of the head-pieces of the elementary particles in the inner mitochondrial membrane, the head-pieces were detached by sonication from the isolated
inner membrane of beef heart mitochondria, purified by pursuing the particles with the electron microscope, and analyzed for enzymatic properties. 2. Electron microscope examination revealed that the isolated headpieces
are the spherical particles about 90À in diameter which are quite similar in appearance to the head-pieces of the elementary particles lining the inner mitochondrial membranes. 3. The head-pieces are identified as ATPase sensitive to oligomysin when attached by stalks to the membrane, and become insensitive when detached or purified from the membrane. 4. The head-piece is labile to cold with respect to ATPase activity and morphology.</p
Probing Elemental Abundances in SNR 1987A Using XMM-Newton
We report on the latest (2007 Jan) observations of supernova remnant (SNR)
1987A from the XMM-Newton mission. Since the 2003 May observations of Haberl et
al. (2006), 11 emission lines have experienced increases in flux by factors ~ 3
to 10, with the 775 eV line of O VIII showing the greatest increase; we have
observed 6 lines of Fe XVII and Fe XVIII previously unreported by XMM-Newton. A
two-shock model representing plasmas in non-equilibrium ionization is fitted to
the EPIC-pn spectra, yielding temperatures of ~ 0.4 and ~ 3 keV, as well as
elemental abundances for N, O, Ne, Mg, Si, S and Fe. We demonstrate that the
abundance ratio of N and O can be constrained to less than ~20% accuracy.
Within the same confidence interval, the same analysis suggests that the C+N+O
abundance varies from ~ 1.1 to 1.4 X 10^-4. Normalizing our obtained abundances
by the Large Magellanic Cloud (LMC) values of Hughes, Hayashi & Koyama (1998),
we find that O, Ne, Mg and Fe are under-abundant, while Si and S are
over-abundant, consistent with the findings of Aschenbach (2007). Such a result
has implications for both the single-star and binary accretion/merger models
for the progenitor of SNR 1987A. In the context of the binary merger scenario
proposed by Morris & Podsiadlowski (2006, 2007), material forming the inner,
equatorial ring was expelled after the merger, implying that either our derived
Fe abundance is inconsistent with typical LMC values or that iron is
under-abundant at the site of the progenitor star of SNR 1987A.Comment: 14 pages, 10 diagrams (2 omitted). Accepted by Ap
Improved large-mode area endlessly single-mode photonic crystal fibers
We numerically study the possibilities for improved large-mode area endlessly
single mode photonic crystal fibers for use in high-power delivery
applications. By carefully choosing the optimal hole diameter we find that a
triangular core formed by three missing neighboring air holes considerably
improves the mode area and loss properties compared to the case with a core
formed by one missing air hole. In a realized fiber we demonstrate an
enhancement of the mode area by ~30 % without a corresponding increase in the
attenuation.Comment: 3 pages including 3 eps-figures. Accepted for Optics Letter
Studies of transverse and longitudinal relaxations of Mn in molecular cluster magnet MnAc
The transverse and longitudinal relaxation rates 1/ and 1/ of
Mn in molecular cluster magnet MnAc have been measured al low
temperatures down to 200mK and in the fields upto 9T. Both of 1/ and
1/ exhibit remarkable decreases with decreasing temperature and with
increasing field, with the relative relation . In the
analysis, we adopt a simple model that the thermal fluctuation of the cluster
spin =10 associated with the spin-phonon interactionis, is only due to the
excitation to the first excited state from the ground state with the average
life-times and (). We show that
1/ is interpreted in terms of the strong collision regime as given by
1/, and that 1/ is understood by the high-frequency limit based
on standard perturbation treatment for the step-wise fluctuating field, thus
being proportional to 1/.Comment: 12 pages, 11 fugures, revtex
Drosophila Parkin requires PINK1 for mitochondrial translocation and ubiquitinates Mitofusin
Loss of the E3 ubiquitin ligase Parkin causes early onset Parkinson's disease, a neurodegenerative disorder of unknown etiology. Parkin has been linked to multiple cellular processes including protein degradation, mitochondrial homeostasis, and autophagy; however, its precise role in pathogenesis is unclear. Recent evidence suggests that Parkin is recruited to damaged mitochondria, possibly affecting mitochondrial fission and/or fusion, to mediate their autophagic turnover. The precise mechanism of recruitment and the ubiquitination target are unclear. Here we show in Drosophila cells that PINK1 is required to recruit Parkin to dysfunctional mitochondria and promote their degradation. Furthermore, PINK1 and Parkin mediate the ubiquitination of the profusion factor Mfn on the outer surface of mitochondria. Loss of Drosophila PINK1 or parkin causes an increase in Mfn abundance in vivo and concomitant elongation of mitochondria. These findings provide a molecular mechanism by which the PINK1/Parkin pathway affects mitochondrial fission/fusion as suggested by previous genetic interaction studies. We hypothesize that Mfn ubiquitination may provide a mechanism by which terminally damaged mitochondria are labeled and sequestered for degradation by autophagy
Novel diffusion mechanism on the GaAs(001) surface: the role of adatom-dimer interaction
Employing first principles total energy calculations we have studied the
behavior of Ga and Al adatoms on the GaAs(001)-beta2 surface. The adsorption
site and two relevant diffusion channels are identified. The channels are
characterized by different adatom-surface dimer interaction. Both affect in a
novel way the adatom migration: in one channel the diffusing adatom jumps
across the surface dimers and leaves the dimer bonds intact, in the other one
the surface dimer bonds are broken. The two channels are taken into account to
derive effective adatom diffusion barriers. From the diffusion barriers we
conclude a strong diffusion anisotropy for both Al and Ga adatoms with the
direction of fastest diffusion parallel to the surface dimers. In agreement
with experimental observations we find higher diffusion barriers for Al than
for Ga.Comment: 4 pages, 2 figures, Phys. Rev. Lett. 79 (1997). Other related
publications can be found at http://www.rz-berlin.mpg.de/th/paper.htm
OPA1 and cardiolipin team up for mitochondrial fusion
Fusion between the inner membranes of two mitochondria requires the GTPase optic atrophy 1 (OPA1), but the molecular mechanism is poorly understood. A study now shows that fusion of two liposomes can be performed by OPA1 tethered to just one liposome, through an interaction with the phospholipid cardiolipin on the opposing liposome
Do Hadronic Charge Exchange Reactions Measure Electroweak L = 1 Strength?
An eikonal model has been used to assess the relationship between calculated
strengths for first forbidden beta decay and calculated cross sections for
(p,n) charge exchange reactions. It is found that these are proportional for
strong transitions, suggesting that hadronic charge exchange reactions may be
useful in determining the spin-dipole matrix elements for astrophysically
interesting leptonic transitions.Comment: 14 pages, 5 figures, Submitted to Physical Review
Astrophysical Axion Bounds
Axion emission by hot and dense plasmas is a new energy-loss channel for
stars. Observational consequences include a modification of the solar
sound-speed profile, an increase of the solar neutrino flux, a reduction of the
helium-burning lifetime of globular-cluster stars, accelerated white-dwarf
cooling, and a reduction of the supernova SN 1987A neutrino burst duration. We
review and update these arguments and summarize the resulting axion
constraints.Comment: Contribution to Axion volume of Lecture Notes in Physics, 20 pages, 3
figure
Computational Indistinguishability between Quantum States and Its Cryptographic Application
We introduce a computational problem of distinguishing between two specific
quantum states as a new cryptographic problem to design a quantum cryptographic
scheme that is "secure" against any polynomial-time quantum adversary. Our
problem, QSCDff, is to distinguish between two types of random coset states
with a hidden permutation over the symmetric group of finite degree. This
naturally generalizes the commonly-used distinction problem between two
probability distributions in computational cryptography. As our major
contribution, we show that QSCDff has three properties of cryptographic
interest: (i) QSCDff has a trapdoor; (ii) the average-case hardness of QSCDff
coincides with its worst-case hardness; and (iii) QSCDff is computationally at
least as hard as the graph automorphism problem in the worst case. These
cryptographic properties enable us to construct a quantum public-key
cryptosystem, which is likely to withstand any chosen plaintext attack of a
polynomial-time quantum adversary. We further discuss a generalization of
QSCDff, called QSCDcyc, and introduce a multi-bit encryption scheme that relies
on similar cryptographic properties of QSCDcyc.Comment: 24 pages, 2 figures. We improved presentation, and added more detail
proofs and follow-up of recent wor
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