4,836 research outputs found
Natural convection with mixed insulating and conducting boundary conditions: low and high Rayleigh numbers regimes
We investigate the stability and dynamics of natural convection in two
dimensions, subject to inhomogeneous boundary conditions. In particular, we
consider a Rayleigh-B\`enard (RB) cell, where the horizontal top boundary
contains a periodic sequence of alternating thermal insulating and conducting
patches, and we study the effects of the heterogeneous pattern on the global
heat exchange, both at low and high Rayleigh numbers. At low Rayleigh numbers,
we determine numerically the transition from a regime characterized by the
presence of small convective cells localized at the inhomogeneous boundary to
the onset of bulk convective rolls spanning the entire domain. Such a
transition is also controlled analytically in the limit when the boundary
pattern length is small compared with the cell vertical size. At higher
Rayleigh number, we use numerical simulations based on a lattice Boltzmann
method to assess the impact of boundary inhomogeneities on the fully turbulent
regime up to
0+ states and collective bands in 228Th studied by the (p,t) reaction
The excitation spectra in the deformed nucleus 228Th have been studied by
means of the (p,t)-reaction, using the Q3D spectrograph facility at the Munich
Tandem accelerator. The angular distributions of tritons were measured for
about 110 excitations seen in the triton spectra up to 2.5 MeV. Firm 0+
assignments are made for 17 excited states by comparison of experimental
angular distributions with the calculated ones using the CHUCK3 code.
Assignments up to spin 6+ are made for other states. Sequences of states are
selected which can be treated as rotational bands and as multiplets of
excitations. Moments of inertia have been derived from these sequences, whose
values may be considered as evidence of the two-phonon nature of most 0+
excitations. Experimental data are compared with interacting boson model and
quasiparticle-phonon model calculations and with experimental data for 229Pa.Comment: 21 pages, 14 figure
Domain wall dynamics in a single CrO grain
Recently we have reported on the magnetization dynamics of a single CrO
grain studied by micro Hall magnetometry (P. Das \textit{et al.}, Appl. Phys.
Lett. \textbf{97} 042507, 2010). For the external magnetic field applied along
the grain's easy magnetization direction, the magnetization reversal takes
place through a series of Barkhausen jumps. Supported by micromagnetic
simulations, the ground state of the grain was found to correspond to a flux
closure configuration with a single cross-tie domain wall. Here, we report an
analysis of the Barkhausen jumps, which were observed in the hysteresis loops
for the external field applied along both the easy and hard magnetization
directions. We find that the magnetization reversal takes place through only a
few configuration paths in the free-energy landscape, pointing to a high purity
of the sample. The distinctly different statistics of the Barkhausen jumps for
the two field directions is discussed.Comment: JEMS Conference, to appear in J. Phys. Conf. Se
Thermo-elasticity for anisotropic media in higher dimensions
In this note we develop tools to study the Cauchy problem for the system of
thermo-elasticity in higher dimensions. The theory is developed for general
homogeneous anisotropic media under non-degeneracy conditions.
For degenerate cases a method of treatment is sketched and for the cases of
cubic media and hexagonal media detailed studies are provided.Comment: 33 pages, 5 figure
Do ultra-runners in a 24-h run really dehydrate?
Background: Loss of body mass during a 24-h run was considered to be a result of dehydration. Aims: We intended to quantify the decrease in body mass as a loss in fat mass or skeletal muscle mass and to quantify the change in hydration status. Methods: Body mass, fat mass, skeletal muscle mass, haematocrit, plasma sodium and urinary specific gravity were measured in 15 ultra-marathoners in a 24-h run. Results: Body mass decreased by 2.2kg (p=0.0009) and fat mass decreased by 0.5kg (p=0.0084). The decrease in body mass correlated to the decrease in fat mass (r=0.72, p=0.0024). Urinary specific gravity increased from 1.012 to 1.022g/mL (p=0.0005). Conclusions: The decrease in body mass and the increase in urinary specific gravity indicate dehydration. The decrease in body mass was correlated to the decrease in fat mass and therefore not only due to dehydratio
Attosecond control of electron dynamics in carbon monoxide
Laser pulses with stable electric field waveforms establish the opportunity
to achieve coherent control on attosecond timescales. We present experimental
and theoretical results on the steering of electronic motion in a
multi-electron system. A very high degree of light-waveform control over the
directional emission of C+ and O+ fragments from the dissociative ionization of
CO was observed. Ab initio based model calculations reveal contributions to the
control related to the ionization and laser-induced population transfer between
excited electronic states of CO+ during dissociation
High spin polarization in the ferromagnetic filled skutterudites KFe4Sb12 and NaFe4Sb12
The spin polarization of ferromagnetic alkali-metal iron antimonides KFe4Sb12
and NaFe4Sb12 is studied by point-contact Andreev reflection using
superconducting Nb and Pb tips. From these measurements an intrinsic transport
spin polarization Pt of 67% and 60% for the K and Na compound, respectively, is
inferred which establishes these materials as a new class of highly spin
polarized ferromagnets. The results are in accord with band structure
calculations within the local spin density approximation (LSDA) that predict
nearly 100% spin polarization in the density of states. We discuss the impact
of calculated Fermi velocities and spin fluctuations on Pt.Comment: Pdf file with fi
An Automatic System to Discriminate Malignant from Benign Massive Lesions on Mammograms
Mammography is widely recognized as the most reliable technique for early
detection of breast cancers. Automated or semi-automated computerized
classification schemes can be very useful in assisting radiologists with a
second opinion about the visual diagnosis of breast lesions, thus leading to a
reduction in the number of unnecessary biopsies. We present a computer-aided
diagnosis (CADi) system for the characterization of massive lesions in
mammograms, whose aim is to distinguish malignant from benign masses. The CADi
system we realized is based on a three-stage algorithm: a) a segmentation
technique extracts the contours of the massive lesion from the image; b)
sixteen features based on size and shape of the lesion are computed; c) a
neural classifier merges the features into an estimated likelihood of
malignancy. A dataset of 226 massive lesions (109 malignant and 117 benign) has
been used in this study. The system performances have been evaluated terms of
the receiver-operating characteristic (ROC) analysis, obtaining A_z =
0.80+-0.04 as the estimated area under the ROC curve.Comment: 6 pages, 3 figures; Proceedings of the ITBS 2005, 3rd International
Conference on Imaging Technologies in Biomedical Sciences, 25-28 September
2005, Milos Island, Greec
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