375 research outputs found
The effect of fasting on the ultrastructure of the hypothalamic arcuate nucleus in young rats
In the present study, we described ultrastructural changes occurring in the
neurons of the hypothalamic arcuate nucleus after food deprivation. Young
male Wistar rats (5 months old, n = 12) were divided into three groups. The
animals in Group I were used as control (normally fed), and the rats in Groups
II and III were fasted for 48 hours and 96 hours, respectively. In both treated
groups, fasting caused rearrangement of the rough endoplasmic reticulum forming
lamellar bodies and membranous whorls. The lamellar bodies were rather
short in the controls, whereas in the fasting animals they became longer and
were sometimes participating in the formation of membranous whorls composed
of the concentric layers of the smooth endoplasmic reticulum. The whorls
were often placed in the vicinity of a very well developed Golgi complex. Some
Golgi complexes displayed an early stage of whorl formation. Moreover, an
increased serum level of 8-isoprostanes, being a reliable marker of total oxidative
stress in the body, was observed in both fasting groups of rats as compared
to the control
Ultrastructural observations on the hypothalamic arcuate nuclei of aged rats in the fasting/refeeding model
The arcuate nucleus of the hypothalamus (ARH) is involved in the control of
energy homeostasis. This is the first study on the ultrastructural response of ARH
neurons in aged rats after short-term fasting and subsequent refeeding. Male
Wistar rats (24 weeks old) were fasted for 48 or 96 hours and were then refed for
24 hours. The controls were normally fed. The rats received water ad libitum. In
both groups of fasting animals, we observed a rearrangement of the arcuate
rough endoplasmic reticulum (RER) and Golgi complexes to form membranous
whorls. Moreover, refeeding for 24 hours did not reverse this process. The RER
was frequently found to be well organized into lamellar bodies composed of
several cisternae. The membranous whorls were composed of concentric layers
of endoplasmic reticulum and Golgi complexes. In addition, multiform lipofuscin
granules were observed in close relationship with Golgi complexes and membranous
whorls. Lipofuscin granules within the neurons of the arcuate nucleus are
assumed to be a morphological manifestation of oxidative stress phenomena,
which are presumably implicated in the formation of membranous whorls in
both fasting and fasting/refed animals. This observation correlates with a significant
increase in 8-isoprostane serum levels in the fasting and fasting/refed animals
as compared to the fed control rats
Nonlocal resistance and its fluctuations in microstructures of band-inverted HgTe/(Hg,Cd)Te quantum wells
We investigate experimentally transport in gated microsctructures containing
a band-inverted HgTe/Hg_{0.3}Cd_{0.7}Te quantum well. Measurements of nonlocal
resistances using many contacts prove that in the depletion regime the current
is carried by the edge channels, as expected for a two-dimensional topological
insulator. However, high and non-quantized values of channel resistances show
that the topological protection length (i.e. the distance on which the carriers
in helical edge channels propagate without backscattering) is much shorter than
the channel length, which is ~100 micrometers. The weak temperature dependence
of the resistance and the presence of temperature dependent reproducible
quasi-periodic resistance fluctuations can be qualitatively explained by the
presence of charge puddles in the well, to which the electrons from the edge
channels are tunnel-coupled.Comment: 8 pages, 4 figures, published versio
Field Effect Transistors for Terahertz Detection: Physics and First Imaging Applications
Resonant frequencies of the two-dimensional plasma in FETs increase with the
reduction of the channel dimensions and can reach the THz range for sub-micron
gate lengths. Nonlinear properties of the electron plasma in the transistor
channel can be used for the detection and mixing of THz frequencies. At
cryogenic temperatures resonant and gate voltage tunable detection related to
plasma waves resonances, is observed. At room temperature, when plasma
oscillations are overdamped, the FET can operate as an efficient broadband THz
detector. We present the main theoretical and experimental results on THz
detection by FETs in the context of their possible application for THz imaging.Comment: 22 pages, 12 figures, review pape
Interferometric probes of many-body localization
We propose a method for detecting many-body localization (MBL) in disordered
spin systems. The method involves pulsed, coherent spin manipulations that
probe the dephasing of a given spin due to its entanglement with a set of
distant spins. It allows one to distinguish the MBL phase from a
non-interacting localized phase and a delocalized phase. In particular, we show
that for a properly chosen pulse sequence the MBL phase exhibits a
characteristic power-law decay reflecting its slow growth of entanglement. We
find that this power-law decay is robust with respect to thermal and disorder
averaging, provide numerical simulations supporting our results, and discuss
possible experimental realizations in solid-state and cold atom systems.Comment: 5 pages, 4 figure
Characterization of Mott-insulating and superfluid phases in the one-dimensional Bose--Hubbard model
We use strong-coupling perturbation theory, the variational cluster approach
(VCA), and the dynamical density-matrix renormalization group (DDMRG) method to
investigate static and dynamical properties of the one-dimensional
Bose--Hubbard model in both the Mott-insulating and superfluid phases. From the
von Neumann entanglement entropy we determine the central charge and the
transition points for the first two Mott lobes. Our DMRG results for the
ground-state energy, momentum distribution function, boson correlation function
decay, Mott gap, and single particle-spectral function are reproduced very well
by the strong-coupling expansion to fifth order, and by VCA with clusters up to
12 sites as long as the ratio between the hopping amplitude and on-site
repulsion, t/U, is smaller than 0.15 and 0.25, respectively. In addition, in
the superfluid phase VCA captures well the ground-state energy and the sound
velocity of the linear phonon modes. This comparison provides an authoritative
estimate for the range of applicability of these methods. In strong-coupling
theory for the Mott phase, the dynamical structure factor is obtained from the
solution of an effective single-particle problem with an attractive potential.
The resulting resonances show up as double-peak structure close to the
Brillouin zone boundary. These high-energy features also appear in the
superfluid phase which is characterized by a pronounced phonon mode at small
momenta and energies, as predicted by Bogoliubov and field theory. In one
dimension, there are no traces of an amplitude mode in the dynamical
single-particle and two-particle correlation functions.Comment: 15 pages, 12 figure
Temperature-induced topological phase transition in HgTe quantum wells
We report a direct observation of temperature-induced topological phase
transition between trivial and topological insulator in HgTe quantum well. By
using a gated Hall bar device, we measure and represent Landau levels in fan
charts at different temperatures and we follow the temperature evolution of a
peculiar pair of "zero-mode" Landau levels, which split from the edge of
electron-like and hole-like subbands. Their crossing at critical magnetic field
is a characteristic of inverted band structure in the quantum well. By
measuring the temperature dependence of , we directly extract the critical
temperature , at which the bulk band-gap vanishes and the topological
phase transition occurs. Above this critical temperature, the opening of a
trivial gap is clearly observed.Comment: 5 pages + Supplemental Materials; Phys. Rev. Lett. (accepted
Ultrastructural response of arcuate nucleus neurons to fasting in aged rats
The arcuate nucleus of the hypothalamus (ARH) is involved in the control of
energy homeostasis. Leptin - an adipocyte derived hormone - is known to
act on the hypothalamic nuclei and thus to control body weight by food intake
reduction. Oxidative stress is believed to be implicated in leptin signalling. However,
its relevance for leptin-induced signal transduction within ARH remains
unclear. The goal of the study was to investigate the effect of fasting on morphological
alterations of the neuronal endoplasmic reticulum/Golgi network as
well as on the expression of leptin receptors in the arcuate nucleus of aged
rats. Male Wistar rats, aged 24 months, were fasted for 96 hours. The control
animals were fed ad libitum. Membranous whorls in the ARH neurons were
visualized using the electron microscopy technique. Leptin receptors in the
membranes of ARH neurons were determined immunohistochemically (IHC),
and soluble leptin receptors in the plasma as well as plasma isoprostanes were
quantified immunochemically (ELISA). An intense formation of membranous
whorls was observed, directly associated with the cisternae of the rough endoplasmic
reticulum, as well as lamellar bodies. Interestingly, the whorls were
often localized near a well-developed Golgi complex. Moreover, some Golgi
complexes displayed an early stage of whorl formation. Groups of residual
lipofuscin granules were found in the immediate proximity of the whorls. An
increased immunoreactivity with neuronal leptin receptors suggests that hypersensitive
neurons may still effectively respond to the fasting serum levels of
leptin, mediating ultrastructural transformation of ARH neurons during short-term fasting. Having observed a significant accumulation of lipofuscin granules
and a marked increase of total 8-isoprostane serum level in the fasting rats, we
hypothesize that signal transduction within the neurons of ARH is dependent
on oxidative stress phenomena
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