601 research outputs found
Hydrodynamic collective effects of active proteins in biological membranes
Lipid bilayers forming biological membranes are known to behave as viscous 2D
fluids on submicrometer scales; usually they contain a large number of active
protein inclusions. Recently, it has been shown [Proc. Nat. Acad. Sci. USA 112,
E3639 (2015)] that such active proteins should in- duce non-thermal fluctuating
lipid flows leading to diffusion enhancement and chemotaxis-like drift for
passive inclusions in biomembranes. Here, a detailed analytical and numerical
investigation of such effects is performed. The attention is focused on the
situations when proteins are concentrated within lipid rafts. We demonstrate
that passive particles tend to become attracted by active rafts and are
accumulated inside them.Comment: 12 pages, 7 figure
Spin-glass-like behavior of Ge:Mn
We present a detailed study of the magnetic properties of
low-temperature-molecular-beam-epitaxy grown Ge:Mn dilute magnetic
semiconductor films. We find strong indications for a frozen state of
Ge_{1-x}Mn_{x}, with freezing temperatures of T_f=12K and T_f=15K for samples
with x=0.04 and x=0.2, respectively, determined from the difference between
field-cooled and zero-field-cooled magnetization. For Ge_{0.96}Mn_{0.04}, ac
susceptibility measurements show a peak around T_f, with the peak position T'_f
shifting as a function of the driving frequency f by Delta T_f' / [T_f' Delta
log f] ~ 0.06, whereas for sample Ge_{0.8}Mn_{0.2} a more complicated behavior
is observed. Furthermore, both samples exhibit relaxation effects of the
magnetization after switching the magnitude of the external magnetic field
below T_f which are in qualitative agreement with the field- and
zero-field-cooled magnetization measurements. These findings consistently show
that Ge:Mn exhibits a frozen magnetic state at low temperatures and that it is
not a conventional ferromagnet.Comment: Revised version contains extended interpretation of experimental dat
Photospheric Abundances of Volatile and Refractory Elements in Planet-Harboring Stars
By using the high-dispersion spectra of 14 bright planet-harboring stars
(along with 4 reference stars) observed with the new coude echelle spectrograph
at Okayama Astrophysical Observatory, we investigated the abundances of
volatile elements (C, N, O, S, Zn; low condensation temperature Tc) in order to
examine whether these show any significant difference compared to the
abundances of other refractory elements (Si, Ti, V, Fe, Co, Ni; high Tc) which
are known to be generally overabundant in those stars with planets, since a
Tc-dependence is expected if the cause of such a metal-richness is due to the
accretion of solid planetesimals onto the host star. We found, however, that
all elements we studied behave themselves quite similarly to Fe (i.e.,
[X/Fe]~0) even for the case of volatile elements, which may suggest that the
enhanced metallicity in those planet-bearing stars is not so much an acquired
character (by accretion of rocky material) as rather primordial.Comment: 22 pages, 8 figures, to appear in PAS
Large Thermoelectric Power Factor in TiS2 Crystal with Nearly Stoichiometric Composition
A TiS crystal with a layered structure was found to have a large
thermoelectric power factor.The in-plane power factor at 300 K is
37.1~W/Kcm with resistivity () of 1.7 mcm and
thermopower () of -251~V/K, and this value is comparable to that of the
best thermoelectric material, BiTe alloy. The electrical
resistivity shows both metallic and highly anisotropic behaviors, suggesting
that the electronic structure of this TiS crystal has a
quasi-two-dimensional nature. The large thermoelectric response can be ascribed
to the large density of state just above the Fermi energy and inter-valley
scattering. In spite of the large power factor, the figure of merit, of
TiS is 0.16 at 300 K, because of relatively large thermal conductivity,
68~mW/Kcm. However, most of this value comes from reducible lattice
contribution. Thus, can be improved by reducing lattice thermal
conductivity, e.g., by introducing a rattling unit into the inter-layer sites.Comment: 11 pages, 4 figures, to be published in Physical Review
Magnetic relaxation phenomena and cluster glass properties of La{0.7-x}Y{x}Ca{0.3}MnO{3} manganites
The dynamic magnetic properties of the distorted perovskite system
La{0.7-x}Y{x}Ca{0.3}MnO{3} (0 <= x <= 0.15) have been investigated by
ac-susceptibility and dc magnetization measurements, with emphasis on
relaxation and aging studies. They evidence for x >= 0.10 the appearance of a
metallic cluster glass phase, that develops just below the ferromagnetic
transition temperature. The clusters grow with decreasing temperature down to a
temperature T(f0) at which they freeze due to severe intercluster frustration.
The formation of these clusters is explained by the presence of yttrium induced
local structural distortions that create localized spin disorder in a magnetic
lattice where double-exchange ferromagnetism is dominant.Comment: Accepted for publication in Phys. Rev.
MITSuME--Multicolor Imaging Telescopes for Survey and Monstrous Explosions
Development of MITSuME is reported. Two 50-cm optical telescopes have been
built at Akeno in Yamanashi prefecture and at Okayama Astrophysical Observatory
(OAO) in Okayama prefecture. Three CCD cameras for simultaneous g'RcIc
photometry are to be mounted on each focal plane, covering a wide FOV of about
30" x 30". The limiting magnitude at V is fainter than 18. In addition to these
two optical telescopes, a 91-cm IR telescope with a 1 deg x 1 deg field of view
is being built at OAO, which performs photometry in YJHK bands. These robotic
telescopes can start the observation of counterparts of a GRB within a minute
from an alert. We aim to obtain photometric redshifts exceeding 10 with these
telescopes. The performance and the current construction status of the
telescopes are presented.Comment: 4 pages, 3 figures, 4th Workshop on Gamma-Ray Burst in the Afterglow
Era, Roma, October 18-22, 200
Electronic structure of Co_xTiSe_2 and Cr_xTiSe_2
The results of investigations of intercalated compounds Cr_xTiSe_2 and
Co_xTiSe_2 by X-ray photoelectron spectroscopy (XPS) and X-ray emission
spectroscopy (XES) are presented. The data obtained are compared with
theoretical results of spin-polarized band structure calculations. A good
agreement between theoretical and experimental data for the electronic
structure of the investigated materials has been observed. The interplay
between the M3d--Ti3d hybridization (M=Cr, Co) and the magnetic moment at the M
site is discussed. A 0.9 eV large splitting of the core Cr2p{3/2} level was
observed, which reveals a strong exchange magnetic interaction of 3d-2p
electrons of Cr. In the case of a strong localization of the Cr3d electrons
(for x<0.25), the broadening of the CrL spectra into the region of the states
above the nominal Fermi level was observed and attributed to X-ray re-emission.
The measured kinetic properties are in good accordance with spectral
investigations and band calculation results.Comment: 14 pages, 11 figures, submitted to Phys.Rev.
VEZF1 elements mediate protection from DNA methylation
There is growing consensus that genome organization and long-range gene regulation involves partitioning of the genome into domains of distinct epigenetic chromatin states. Chromatin insulator or barrier elements are key components of these processes as they can establish boundaries between chromatin states. The ability of elements such as the paradigm β-globin HS4 insulator to block the range of enhancers or the spread of repressive histone modifications is well established. Here we have addressed the hypothesis that a barrier element in vertebrates should be capable of defending a gene from silencing by DNA methylation. Using an established stable reporter gene system, we find that HS4 acts specifically to protect a gene promoter from de novo DNA methylation. Notably, protection from methylation can occur in the absence of histone acetylation or transcription. There is a division of labor at HS4; the sequences that mediate protection from methylation are separable from those that mediate CTCF-dependent enhancer blocking and USF-dependent histone modification recruitment. The zinc finger protein VEZF1 was purified as the factor that specifically interacts with the methylation protection elements. VEZF1 is a candidate CpG island protection factor as the G-rich sequences bound by VEZF1 are frequently found at CpG island promoters. Indeed, we show that VEZF1 elements are sufficient to mediate demethylation and protection of the APRT CpG island promoter from DNA methylation. We propose that many barrier elements in vertebrates will prevent DNA methylation in addition to blocking the propagation of repressive histone modifications, as either process is sufficient to direct the establishment of an epigenetically stable silent chromatin stat
Aflatoxin contamination in Tanzania: quantifying the problem in maize and groundnuts from rural households
Published online: 28 Apr 2021Aflatoxins are toxic and carcinogenic secondary metabolites, produced by Aspergillus flavus and Aspergillus parasiticus, which contaminate food and feed and threaten human and animal health. To assess the prevalence of aflatoxins in Tanzania, 180 groundnut and 200 maize samples were collected from 9 and 10 districts, respectively. Aflatoxin contamination was quantified using high performance liquid chromatography. Aflatoxins were detected in samples collected from all districts and prevalence ranged from 92 to 100% for groundnuts and 10 to 80% for maize. The mean aflatoxin level for groundnuts was 6.37 μg/kg and the highly contaminated sample had 40.31 μg/kg. For maize, the mean aflatoxin level was 12.47 μg/kg and the highly contaminated sample had 162.40 μg/kg. The estimated average probable daily intake (APDI) of aflatoxin B1 (AFB1) from groundnuts consumption was 1.88 ng/kg body weight/day, while for maize, it ranged between 151.98-272.89 ng/kg body weight/day. The APDI for both groundnut and maize exceeded the provisional maximum tolerable daily intake (PMTDI) of AFB1 for adults (1 ng/kg body weight/day), bringing about health concerns for populations in Tanzania. Another alarming finding was that 75% of the farmers who provided samples for analysis were not aware of aflatoxins or the negative health impacts from consuming contaminated products. Results reported in this paper show that aflatoxin contaminated staple crops are widely distributed in Tanzania and that the risk of human exposure is high due to diet preferences. Awareness campaigns are required to inform and protect farmers and consumers
Diurnal Variation of Human Sweet Taste Recognition Thresholds Is Correlated With Plasma Leptin Levels
OBJECTIVE—It has recently been proposed that the peripheral taste organ is one of the targets for leptin. In lean mice, leptin selectively suppresses gustatory neural and behavioral responses to sweet compounds without affecting responses to other taste stimuli, whereas obese diabetic db/db mice with defects in leptin receptor lack this leptin suppression on sweet taste. Here, we further examined potential links between leptin and sweet taste in humans
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