2,087 research outputs found
Heat shock factor 1 regulates lifespan as distinct from disease onset in prion disease
Prion diseases are fatal, transmissible, neurodegenerative diseases caused by the misfolding of the prion protein (PrP). At present, the molecular pathways underlying prion-mediated neurotoxicity are largely unknown. We hypothesized that the transcriptional regulator of the stress response, heat shock factor 1 (HSF1), would play an important role in prion disease. Uninoculated HSF1 knockout (KO) mice used in our study do not show signs of neurodegeneration as assessed by survival, motor performance, or histopathology. When inoculated with Rocky Mountain Laboratory (RML) prions HSF1 KO mice had a dramatically shortened lifespan, succumbing to disease â20% faster than controls. Surprisingly, both the onset of home-cage behavioral symptoms and pathological alterations occurred at a similar time in HSF1 KO and control mice. The accumulation of proteinase K (PK)-resistant PrP also occurred with similar kinetics and prion infectivity accrued at an equal or slower rate. Thus, HSF1 provides an important protective function that is specifically manifest after the onset of behavioral symptoms of prion disease
Signal to noise ratio in parametrically-driven oscillators
Here we report a theoretical model based on Green's functions and averaging
techniques that gives ana- lytical estimates to the signal to noise ratio (SNR)
near the first parametric instability zone in parametrically- driven
oscillators in the presence of added ac drive and added thermal noise. The
signal term is given by the response of the parametrically-driven oscillator to
the added ac drive, while the noise term has two dif- ferent measures: one is
dc and the other is ac. The dc measure of noise is given by a time-average of
the statistically-averaged fluctuations of the position of the parametric
oscillator due to thermal noise. The ac measure of noise is given by the
amplitude of the statistically-averaged fluctuations at the frequency of the
parametric pump. We observe a strong dependence of the SNR on the phase between
the external drive and the parametric pump, for some range of the phase there
is a high SNR, while for other values of phase the SNR remains flat or
decreases with increasing pump amplitude. Very good agreement between
analytical estimates and numerical results is achieved.Comment: Submitted to Phys. Rev.
Approximate Quantum Fourier Transform and Decoherence
We discuss the advantages of using the approximate quantum Fourier transform
(AQFT) in algorithms which involve periodicity estimations. We analyse quantum
networks performing AQFT in the presence of decoherence and show that extensive
approximations can be made before the accuracy of AQFT (as compared with
regular quantum Fourier transform) is compromised. We show that for some
computations an approximation may imply a better performance.Comment: 14 pages, 10 fig. (8 *.eps files). More information on
http://eve.physics.ox.ac.uk/QChome.html
http://www.physics.helsinki.fi/~kasuomin
http://www.physics.helsinki.fi/~kira/group.htm
Magnetic Field Effects on the Structure and Evolution of Overdense Radiatively Cooling Jets
We investigate the effect of magnetic fields on the propagation dynamics and
morphology of overdense, radiatively cooling, supermagnetosonic jets, with the
help of fully three-dimensional SPMHD simulations. Evaluated for a set of
parameters which are mainly suitable for protostellar jets (with density ratios
between the jet and the ambient medium 3-10, and ambient Mach number ~ 24),
these simulations are also compared with baseline non-magnetic and adiabatic
calculations. We find that, after amplification by compression and
re-orientation in nonparallel shocks at the working surface, the magnetic field
that is carried backward with the shocked gas into the cocoon improves the jet
collimation relative to the purely hydrodynamic (HD) systems. Low-amplitude,
approximately equally spaced internal shocks (which are absent in the HD
systems) are produced by MHD K-H reflection pinch modes. The longitudinal field
geometry also excites non-axisymmetric helical modes which cause some beam
wiggling. The strength and amount of these modes are, however, reduced (by ~
twice) in the presence of radiative cooling relative to the adiabatic cases.
Besides, a large density ratio between the jet and the ambient medium also
reduces, in general, the number of the internal shocks. As a consequence, the
weakness of the induced internal shocks makes it doubtful that the magnetic
pinches could produce by themselves the bright knots observed in the overdense,
radiatively cooling protostellar jets.Comment: To appear in ApJ; 36 pages + 16 (gif) figures. PostScript files of
figures are available at http://www.iagusp.usp.br/preprints/preprint.htm
Conditional Quantum Dynamics and Logic Gates
Quantum logic gates provide fundamental examples of conditional quantum
dynamics. They could form the building blocks of general quantum information
processing systems which have recently been shown to have many interesting
non--classical properties. We describe a simple quantum logic gate, the quantum
controlled--NOT, and analyse some of its applications. We discuss two possible
physical realisations of the gate; one based on Ramsey atomic interferometry
and the other on the selective driving of optical resonances of two subsystems
undergoing a dipole--dipole interaction.Comment: 5 pages, RevTeX, two figures in a uuencoded, compressed fil
Pharmacological Modulation of Three Modalities of CA1 Hippocampal Long-Term Potentiation in the Ts65Dn Mouse Model of Down Syndrome
The Ts65Dn mouse is the most studied animal model of Down syndrome. Past research has shown a significant reduction in CA1 hippocampal long-term potentiation (LTP) induced by theta-burst stimulation (TBS), but not in LTP induced by high-frequency stimulation (HFS), in slices from Ts65Dn mice compared with euploid mouse-derived slices. Additionally, therapeutically relevant doses of the drug memantine were shown to rescue learning and memory deficits in Ts65Dn mice. Here, we observed that 1 mu M memantine had no detectable effect on HFS-induced LTP in either Ts65Dn- or control-derived slices, but it rescued TBS-induced LTP in Ts65Dn-derived slices to control euploid levels. Then, we assessed LTP induced by four HFS (4xHFS) and found that this form of LTP was significantly depressed in Ts65Dn slices when compared with LTP in euploid control slices. Memantine, however, did not rescue this phenotype. Because 4xHFS-induced LTP had not yet been characterized in Ts65Dn mice, we also investigated the effects of picrotoxin, amyloid beta oligomers, and soluble recombinant human prion protein (rPrP) on this form of LTP. Whereas >= 10 mu M picrotoxin increased LTP to control levels, it also caused seizure-like oscillations. Neither amyloid beta oligomers nor rPrP had any effect on 4xHFS-induced LTP in Ts65Dn-derived slices.Alana USA Foundation [124124]Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES)Awakening AngelsNIH [NS083687]Case Western Reserve Univ, Dept Pediat, Div Pediat Neurol, Cleveland, OH 44106 USAUniv Fed Sao Paulo, Cardiol, Postgrad Program Med, BR-04024002 Sao Paulo, SP, BrazilCase Western Reserve Univ, Dept Physiol & Biophys, Cleveland, OH 44106 USACase Western Reserve Univ, Dept Psychiat, Cleveland, OH 44106 USAUniv Fed Sao Paulo, Cardiol, Postgrad Program Med, BR-04024002 Sao Paulo, SP, BrazilCAPES: NS083687Web of Scienc
Parallel processing in immune networks
In this work we adopt a statistical mechanics approach to investigate basic,
systemic features exhibited by adaptive immune systems. The lymphocyte network
made by B-cells and T-cells is modeled by a bipartite spin-glass, where,
following biological prescriptions, links connecting B-cells and T-cells are
sparse. Interestingly, the dilution performed on links is shown to make the
system able to orchestrate parallel strategies to fight several pathogens at
the same time; this multitasking capability constitutes a remarkable, key
property of immune systems as multiple antigens are always present within the
host. We also define the stochastic process ruling the temporal evolution of
lymphocyte activity, and show its relaxation toward an equilibrium measure
allowing statistical mechanics investigations. Analytical results are compared
with Monte Carlo simulations and signal-to-noise outcomes showing overall
excellent agreement. Finally, within our model, a rationale for the
experimentally well-evidenced correlation between lymphocytosis and
autoimmunity is achieved; this sheds further light on the systemic features
exhibited by immune networks.Comment: 21 pages, 9 figures; to appear in Phys. Rev.
Spin rotation induced by applied pressure in the Cd-doped Ce2RhIn8 intermetallic compound
FAPESP - FUNDAĂĂO DE AMPARO Ă PESQUISA DO ESTADO DE SĂO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTĂFICO E TECNOLĂGICOCAPES - COORDENAĂĂO DE APERFEIĂOAMENTO DE PESSOAL DE NĂVEL SUPERIORThe pressure evolution of the magnetic properties of the Ce2RhIn7.79Cd0.21 heavy fermion compound was investigated by single crystal neutron magnetic diffraction and electrical resistivity experiments under applied pressure. From the neutron magnetic diffraction data, up to P = 0.6 GPa, we found no changes in the magnetic structure or in the ordering temperature T-N = 4.8 K. However, the increase of pressure induces an interesting spin rotation of the ordered antiferromagnetic moment of Ce2RhIn7.79Cd0.21 into the ab tetragonal plane. From the electrical resistivity measurements under pressure, we have mapped the evolution of T-N and the maximum of the temperature dependent electrical resistivity (T-MAX) as a function of the pressure (P less than or similar to 3.6 GPa). To gain some insight into the microscopic origin of the observed spin rotation as a function of pressure, we have also analyzed some macroscopic magnetic susceptibility data at ambient pressure for pure and Cd-doped Ce2RhIn8 using a mean-field model including tetragonal crystalline electric field (CEF). The analysis indicates that these compounds have a Kramers doublet Gamma(-)(7)-type ground state, followed by a Gamma(+)(7) first excited state at Delta(1) similar to 80 K and a Gamma(6) second excited state at Delta(2) similar to 270 K for Ce2RhIn8 and Delta(2) similar to 250 K for Ce2RhIn7.79Cd0.21. The evolution of the magnetic properties of Ce2RhIn8 as a function of Cd doping and the rotation of the direction of the ordered moment for the Ce2RhIn7.79Cd0.21 compound under pressure suggest important changes of the single ion anisotropy of Ce3+ induced by applying pressure and Cd doping in these systems. These changes are reflected in modifications in the CEF scheme that will ultimately affect the actual ground state of these compounds.1001616FAPESP - FUNDAĂĂO DE AMPARO Ă PESQUISA DO ESTADO DE SĂO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTĂFICO E TECNOLĂGICOCAPES - COORDENAĂĂO DE APERFEIĂOAMENTO DE PESSOAL DE NĂVEL SUPERIORFAPESP - FUNDAĂĂO DE AMPARO Ă PESQUISA DO ESTADO DE SĂO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTĂFICO E TECNOLĂGICOCAPES - COORDENAĂĂO DE APERFEIĂOAMENTO DE PESSOAL DE NĂVEL SUPERIOR2006/60440-02009/09247-32017/10581-12019/04196-3Sem informaçãoSem informaçã
Non-invasive detection of the evolution of the charge states of a double dot system
Coupled quantum dots are potential candidates for qubit systems in quantum
computing. We use a non-invasive voltage probe to study the evolution of a
coupled dot system from a situation where the dots are coupled to the leads to
a situation where they are isolated from the leads. Our measurements allow us
to identify the movement of electrons between the dots and we can also identify
the presence of a charge trap in our system by detecting the movement of
electrons between the dots and the charge trap. The data also reveals evidence
of electrons moving between the dots via excited states of either the single
dots or the double dot molecule.Comment: Accepted for publication in Phys. Rev. B. 4 pages, 4 figure
Bloch bundles, Marzari-Vanderbilt functional and maximally localized Wannier functions
We consider a periodic Schroedinger operator and the composite Wannier
functions corresponding to a relevant family of its Bloch bands, separated by a
gap from the rest of the spectrum. We study the associated localization
functional introduced by Marzari and Vanderbilt, and we prove some results
about the existence and exponential localization of its minimizers, in
dimension d < 4. The proof exploits ideas and methods from the theory of
harmonic maps between Riemannian manifolds.Comment: 37 pages, no figures. V2: the appendix has been completely rewritten.
V3: final version, to appear in Commun. Math. Physic
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