998 research outputs found
Engineering Entanglement: The Fast-Approach Phase Gate
Optimal-control techniques and a fast-approach scheme are used to implement a
collisional control phase gate in a model of cold atoms in an optical lattice,
significantly reducing the gate time as compared to adiabatic evolution while
maintaining high fidelity. New objective functionals are given for which
optimal paths are obtained for evolution that yields a control-phase gate up to
single-atom Rabi shifts. Furthermore, the fast-approach procedure is used to
design a path to significantly increase the fidelity of non-adiabatic transport
in a recent experiment. Also, the entanglement power of phase gates is
quantified.Comment: 7 pages, 4 figures. Phys. Rev. A (in press
Using subthreshold events to characterize the functional architecture of the electrically coupled inferior olive network
The electrical connectivity in the inferior olive (IO) nucleus plays an important role in generating well-timed spiking activity. Here we combined electrophysiological and computational approaches to assess the functional organization of the IO nucleus in mice. Spontaneous fast and slow subthreshold events were commonly encountered during in vitro recordings. We show that whereas the fast events represent intrinsic regenerative activity, the slow events reflect the electrical connectivity between neurons ('spikelets'). Recordings from cell pairs revealed the synchronized occurrence of distinct groups of spikelets; their rate and distribution enabled an accurate estimation of the number of connected cells and is suggestive of a clustered organization. This study thus provides a new perspective on the functional and structural organization of the olivary nucleus and a novel experimental and theoretical approach to study electrically coupled networks
Pattern Competition in the Photorefractive Semiconductors
We analytically study the photorefractive Gunn effect in n-GaAs subjected to
two external laser beams which form a moving interference pattern (MIP) in the
semiconductor. When the intensity of the spatially independent part of the MIP,
denoted by , is small, the system has a periodic domain train (PDT),
consistent with the results of linear stability analysis. When is large,
the space-charge field induced by the MIP will compete with the PDT and result
in complex dynamics, including driven chaos via quasiperiodic route
Suppression of geometrical barrier in crystals by Josephson vortex stacks
Differential magneto-optics are used to study the effect of dc in-plane
magnetic field on hysteretic behavior due to geometrical barriers in
crystals. In absence of in-plane field a vortex
dome is visualized in the sample center surrounded by barrier-dominated
flux-free regions. With in-plane field, stacks of Josephson vortices form
vortex chains which are surprisingly found to protrude out of the dome into the
vortex-free regions. The chains are imaged to extend up to the sample edges,
thus providing easy channels for vortex entry and for drain of the dome through
geometrical barrier, suppressing the magnetic hysteresis. Reduction of the
vortex energy due to crossing with Josephson vortices is evaluated to be about
two orders of magnitude too small to account for the formation of the
protruding chains. We present a model and numerical calculations that
qualitatively describe the observed phenomena by taking into account the
demagnetization effects in which flux expulsion from the pristine regions
results in vortex focusing and in the chain protrusion. Comparative
measurements on a sample with narrow etched grooves provide further support to
the proposed model.Comment: 12 figures (low res.) Higher resolution figures are available at the
Phys Rev B version. Typos correcte
Duretovo krvarenje: rijetka komplikacija ishemijskog moždanog udara u podruÄju srediÅ”nje moždane arterije - Prikaz sluÄaja
We report on an unusual case of brainstem Duret hemorrhage after ischemic stroke in the anterior circulation. The patient showed a clinical and neuroradiological picture of an acute and malignant middle cerebral artery infarct with increased intracranial pressure followed by a brainstem hemorrhage. The report suggests that the descending transtentorial herniation of any etiology might be complicated by a Duret hemorrhage.Opisuje se rijedak sluÄaj Duretova krvarenja moždanoga debla nakon ishemijskog moždanog udara u prednjem krvotoku. Bolesnik je pokazivao kliniÄku i neuroradioloÅ”ku sliku akutnog i zloÄudnog infarkta srediÅ”nje moždane arterije uz poviÅ”en intrakranijski tlak, nakon Äega je uslijedilo krvarenje u moždanom deblu. Ovaj prikaz ukazuje na to da se Duretovo krvarenje može pojaviti kao komplikacija kod silazne transtentorijske hernijacije bilo koje etiologije
- ā¦