2,274 research outputs found
A small tabletop experiment for a direct measurement of the speed of light
A small tabletop experiment for a direct measurement of the speed of light to
an accuracy of few percent is described. The experiment is accessible to a wide
spectrum of undergraduate students, in particular to students not majoring in
science or engineering. The experiment may further include a measurement of the
index of refraction of a sample. Details of the setup and equipment are given.
Results and limitations of the experiment are analyzed, partly based on our
experience in employing the experiment in our student laboratories. Safety
considerations are also discussed.Comment: 4pages, 5fig
Domain Size Dependence of Piezoelectric Properties of Ferroelectrics
The domain size dependence of piezoelectric properties of ferroelectrics is
investigated using a continuum Ginzburg-Landau model that incorporates the
long-range elastic and electrostatic interactions. Microstructures with desired
domain sizes are created by quenching from the paraelectric phase by biasing
the initial conditions. Three different two-dimensional microstructures with
different sizes of the domains are simulated. An electric field is
applied along the polar as well as non-polar directions and the piezoelectric
response is simulated as a function of domain size for both cases. The
simulations show that the piezoelectric coefficients are enhanced by reducing
the domain size, consistent with recent experimental results of Wada and
Tsurumi (Brit. Ceram. Trans. {\bf 103}, 93, 2004) on domain engineered
Comment: submitted to Physical Review
Dynamics of Multiferroic Domain Wall in Spin-Cycloidal Ferroelectric DyMnO
We report the dielectric dispersion of the giant magnetocapacitance (GMC) in
multiferroic DyMnO over a wide frequency range. The GMC is found to be
attributable not to the softened electromagnon but to the electric-field-driven
motion of multiferroic domain wall (DW). In contrast to conventional
ferroelectric DWs, the present multiferroic DW motion holds extremely high
relaxation rate of s even at low temperatures. This
mobile nature as well as the model simulation suggests that the multiferroic DW
is not atomically thin as in ferroelectrics but thick, reflecting its magnetic
origin.Comment: 4 pages, 4 figure
Noise spectroscopy of optical microcavity
The intensity noise spectrum of the light passed through an optical
microcavity is calculated with allowance for thermal fluctuations of its
thickness. The spectrum thus obtained reveals a peak at the frequency of
acoustic mode localized inside the microcavity and depends on the size of the
illuminated area. The estimates of the noise magnitude show that it can be
detected using the up-to-date noise spectroscopy technique.Comment: 10 pages, 1 figur
Specific loss of chondromodulin-I gene expression in chondrosarcoma and the suppression of tumor angiogenesis and growth by its recombinant protein in vivo
AbstractChondromodulin-I (ChM-I) was previously identified as an angiogenesis inhibitor in cartilage. Here, we demonstrated that the level of ChM-I transcripts was substantially reduced to 100 or even less in the lower-grade chondrosarcomas, in articular cartilage or other benign cartilage tumors. We implanted human chondrosarcoma OUMS-27 cells into nude mice that reproducibly produced tumors with cartilaginous matrix. Tumor-induced angiogenesis was evident when the tumors were excised 30 days after implantation. However, the local administration of recombinant human ChM-I almost completely blocked vascular invasion and tumor growth in vivo. Moreover, ChM-I also inhibited the growth of HT-29 colon adenocarcinoma in vivo, implying its therapeutic potential for solid tumors
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Keratoconus and granular dystrophy
Concurrent bilateral keratoconus and granular dystrophy is reported in a 32 year old patient with decreased vision. Initially contact lenses were attempted unsuccessfully to treat the conditions. There are a handful of other reports of these combined pathologies in the literature, and the likelihood of a chance cause or possible genetic linkage between the conditions is discussed
Competition Between Exchange and Anisotropy in a Pyrochlore Ferromagnet
The Ising-like spin ice model, with a macroscopically degenerate ground
state, has been shown to be approximated by several real materials. Here we
investigate a model related to spin ice, in which the Ising spins are replaced
by classical Heisenberg spins. These populate a cubic pyrochlore lattice and
are coupled to nearest neighbours by a ferromagnetic exchange term J and to the
local axes by a single-ion anisotropy term D. The near neighbour spin
ice model corresponds to the case D/J infinite. For finite D/J we find that the
macroscopic degeneracy of spin ice is broken and the ground state is
magnetically ordered into a four-sublattice structure. The transition to this
state is first-order for D/J > 5 and second-order for D/J < 5 with the two
regions separated by a tricritical point. We investigate the magnetic phase
diagram with an applied field along [1,0,0] and show that it can be considered
analogous to that of a ferroelectric.Comment: 7 pages, 4 figure
Abrupt appearance of the domain pattern and fatigue of thin ferroelectric films
We study the domain structure in ferroelectric thin films with a `passive'
layer (material with damaged ferroelectric properties) at the interface between
the film and electrodes within a continuous medium approximation. An abrupt
transition from a monodomain to a polydomain state has been found with the
increase of the `passive' layer thickness . The domain width changes very
quickly at the transition (exponentially with ). We have estimated the
dielectric response (the slope of the hysteresis loop) in the
`fatigued' multidomain state and found that it is in agreement with experiment,
assuming realistic parameters of the layer. We derive a simple universal
relation for the dielectric response, which scales as , involving only the
properties of the passive layer. This relation qualitatively reproduces the
evolution of the hysteresis loop in fatigued samples and it could be tested
with controlled experiments. It is expected that the coercive field should
increase with decreasing lateral size of the film. We believe that specific
properties of the domain structure under bias voltage in ferroelectrics with a
passive layer can resolve the long-standing `paradox of the coercive field'.Comment: 5 pages, REVTeX 3.1 with two eps-figures. Minor amendments. To appear
in Phys. Rev. Letter
A numerical experiment of a polar low observed over the Barents Sea in January 2011
第3回極域科学シンポジウム/特別セッション「これからの北極研究」11月28日(水) 国立極地研究所 2階大会議
Matter Effects in Atmospheric Neutrino Oscillations
The Kamiokande II and IMB data on contained events induced by atmospheric
neutrinos exhibit too low a ratio of muons to electrons, which has been
interpreted as a possible indication of neutrino oscillations. At the same
time, the recent data on upward--going muons in underground detectors have
shown no evidence for neutrino oscillations, strongly limiting the allowed
region of oscillation parameter space. In this paper we confront different
types of neutrino oscillation hypotheses with the experimental results. The
matter effects in and in oscillations are discussed and shown to affect
significantly the upward--going muons.Comment: LaTeX, 13 pages, 4 figures (appended as postscript file in the end of
the paper, one should cut them and process separately), Roma n. 91
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