6,286 research outputs found
APP Expression in Primary Neuronal Cell Cultures fromP6 Mice during in vitro Differentiation
Primary neuronal cell cultures from P6 mice were investigated in order to study amyloid protein precursor (APP) gene expression in differentiating neurons. Cerebellar granule cells which strongly express APP 695 allowed the identification of three distinct isoforms of neuronal APP 695. The high-molecular-weight form of APP 695 is sialylated. The expression pattern of neuronal APP 695 changes during in vitro differentiation. Sialylated forms become more abundant upon longer cultivation time. The secreted forms of sialylated, neuronal APP 695 are shown to comigrate with APP isolated from cerebrospinal fluid. We suggest that the different sialylation states of APP 695 may reflect the modulation of cell-cell and cell-substrate interactions during in vitro differentiation and regeneration
Improving Trip- and Slip-Resisting Skills in Older People: Perturbation Dose Matters
Aging negatively affects balance recovery responses after trips and slips. We hypothesize that older people can benefit from brief treadmill-based trip and slip perturbation exposure despite reduced muscular capacities, but with neuropathology, their responsiveness to these perturbations will be decreased. Thus, to facilitate long-term benefits and their generalizability to everyday life, one needs to consider the individual threshold for perturbation dose.
This is a non-final version of an article published in final form in Exercise and Sport Sciences Review
Cotunneling at resonance for the single-electron transistor
We study electron transport through a small metallic island in the
perturbative regime. Using a recently developed diagrammatic technique, we
calculate the occupation of the island as well as the conductance through the
transistor in forth order in the tunneling matrix elements, a process referred
to as cotunneling. Our formulation does not require the introduction of a
cut-off. At resonance we find significant modifications of previous theories
and good agreement with recent experiments.Comment: 5 pages, Revtex, 5 eps-figure
Solidifying system of democracy in the Central and Eastern European new EU members
The paper examines the requirements of an effective and legitimized democratic political system in the process of transition. The analysis and the conclusions are based on the Hungarian experience, which can carefully be applied to all Central and Eastern European (CEE) countries. Special focus is given to the relationship of legal certainty and the efficiency of the democratic system, to the tension between legalism and managerialism and to the characteristics of civil society organizations. In the conclusion special features of the transitional countries are pointed out
Retention and generalizability of balance recovery response adaptations from trip-perturbations across the adult lifespan
For human locomotion, varying environments require adjustments of the motor system. We asked whether age affects gait balance recovery adaptation, its retention over months and the transfer of adaptation to an untrained reactive balance task. Healthy adults (26 young, 27 middle-aged and 25 older; average ages 24, 52 and 72 years respectively) completed two tasks. The primary task involved treadmill walking: either unperturbed (control; n=39) or subject to unexpected trip perturbations (training; n=39). A single trip perturbation was repeated after a 14-week retention period. The secondary transfer task, before and after treadmill walking, involved sudden loss of balance in a lean-and-release protocol. For both tasks the anteroposterior margin of stability (MoS) was calculated at foot touchdown. For the first (i.e. novel) trip, older adults required one more recovery step ( P=0.03) to regain positive MoS compared to younger, but not middle-aged, adults. However, over several trip perturbations, all age groups increased their MoS for the first recovery step to a similar extent (up to 70%), and retained improvements over 14 weeks, though a decay over time was found for older adults ( P=0.002; middle-aged showing a tendency for decay: P=0.076). Thus, although adaptability in reactive gait stability control remains effective across the adult lifespan, retention of adaptations over time appears diminished with aging. Despite these robust adaptations, the perturbation training group did not show superior improvements in the transfer task compared to aged-matched controls (no differences in MoS changes), suggesting that generalizability of acquired fall-resisting skills from gait-perturbation training may be limited
Intrinsic hole localization mechanism in magnetic semiconductors
The interplay between clustering and exchange coupling in magnetic
semiconductors for the prototype (Ga_{1-x},Mn_x)As with manganese
concentrations x of 1/16 and 1/32 in the interesting experimental range is
investigated. For x ~ 6 %, when all possible arrangements of two atoms within a
large supercell are considered, the clustering of Mn atoms at nearest-neighbour
Ga sites is energetically preferred. As shown by spin density analysis, this
minimum energy configuration localizes further one hole and reduces the
effective charge carrier concentration. Also the exchange coupling constant
increases to a value corresponding to lower Mn concentrations with decreasing
inter Mn distance.Comment: Accepted for publication in Journal of Physics: Condensed Matte
Indirect Exchange Interaction between two Quantum Dots in an Aharonov-Bohm Ring
We investigate the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between
two spins located at two quantum dots embedded in an Aharonov-Bohm (AB) ring.
In such a system the RKKY interaction, which oscillates as a function of the
distance between two local spins, is affected by the flux. For the case of the
ferromagnetic RKKY interaction, we find that the amplitude of AB oscillations
is enhanced by the Kondo correlations and an additional maximum appears at half
flux, where the interaction is switched off. For the case of the
antiferromagnetic RKKY interaction, we find that the phase of AB oscillations
is shifted by pi, which is attributed to the formation of a singlet state
between two spins for the flux value close to integer value of flux.Comment: 10 pages, 5 figure
Charge Fluctuations in the Single Electron Box
Quantum fluctuations of the charge in the single electron box are
investigated. Based on a diagrammatic expansion we calculate the average island
charge number and the effective charging energy in third order in the tunneling
conductance. Near the degeneracy point where the energy of two charge states
coincides, the perturbative approach fails, and we explicitly resum the leading
logarithmic divergencies to all orders. The predictions for zero temperature
are compared with Monte Carlo data and with recent renormalization group
results. While good agreement between the third order result and numerical data
justifies the perturbative approach in most of the parameter regime relevant
experimentally, near the degeneracy point and at zero temperature the
resummation is shown to be insufficient to describe strong tunneling effects
quantitatively. We also determine the charge noise spectrum employing a
projection operator technique. Former perturbative and semiclassical results
are extended by the approach.Comment: 20 pages, 15 figure
Kondo quantum dot coupled to ferromagnetic leads: Numerical renormalization group study
We systematically study the influence of ferromagnetic leads on the Kondo
resonance in a quantum dot tuned to the local moment regime. We employ Wilson's
numerical renormalization group method, extended to handle leads with a spin
asymmetric density of states, to identify the effects of (i) a finite spin
polarization in the leads (at the Fermi-surface), (ii) a Stoner splitting in
the bands (governed by the band edges) and (iii) an arbitrary shape of the
leads density of states. For a generic lead density of states the quantum dot
favors being occupied by a particular spin-species due to exchange interaction
with ferromagnetic leads leading to a suppression and splitting of the Kondo
resonance. The application of a magnetic field can compensate this asymmetry
restoring the Kondo effect. We study both the gate-voltage dependence (for a
fixed band structure in the leads) and the spin polarization dependence (for
fixed gate voltage) of this compensation field for various types of bands.
Interestingly, we find that the full recovery of the Kondo resonance of a
quantum dot in presence of leads with an energy dependent density of states is
not only possible by an appropriately tuned external magnetic field but also
via an appropriately tuned gate voltage. For flat bands simple formulas for the
splitting of the local level as a function of the spin polarization and gate
voltage are given.Comment: 18 pages, 18 figures, accepted for publication in PR
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