1,466 research outputs found
Time frequency analysis in terahertz pulsed imaging
Recent advances in laser and electro-optical technologies have made the previously under-utilized terahertz frequency band of the electromagnetic spectrum
accessible for practical imaging. Applications are emerging, notably in the biomedical domain. In this chapter the technique of terahertz pulsed imaging is
introduced in some detail. The need for special computer vision methods, which arises from the use of pulses of radiation and the acquisition of a time series at
each pixel, is described. The nature of the data is a challenge since we are interested not only in the frequency composition of the pulses, but also how these differ for different parts of the pulse. Conventional and short-time Fourier transforms and wavelets were used in preliminary experiments on the analysis of terahertz
pulsed imaging data. Measurements of refractive index and absorption coefficient were compared, wavelet compression assessed and image classification by multidimensional
clustering techniques demonstrated. It is shown that the timefrequency methods perform as well as conventional analysis for determining material properties. Wavelet compression gave results that were robust through compressions that used only 20% of the wavelet coefficients. It is concluded that the time-frequency methods hold great promise for optimizing the extraction of the spectroscopic information contained in each terahertz pulse, for the analysis of more complex signals comprising multiple pulses or from recently introduced acquisition techniques
Optical properties of tissue measured using terahertz pulsed imaging.
The first demonstrations of terahertz imaging in biomedicine were made several years ago, but few data are available on the optical properties of human tissue at terahertz frequencies. A catalogue of these properties has been established to estimate variability and determine the practicality of proposed medical applications in terms of penetration depth, image contrast and reflection at boundaries. A pulsed terahertz imaging system with a useful bandwidth 0.5-2.5 THz was used. Local ethical committee approval was obtained. Transmission measurements were made through tissue slices of thickness 0.08 to 1 mm, including tooth enamel and dentine, cortical bone, skin, adipose tissue and striated muscle. The mean and standard deviation for refractive index and linear attenuation coefficient, both broadband and as a function of frequency, were calculated. The measurements were used in simple models of the transmission, reflection and propagation of terahertz radiation in potential medical applications. Refractive indices ranged from 1.5 ± 0.5 for adipose tissue to 3.06 ± 0.09 for tooth enamel. Significant differences (P<0.05) were found between the broadband refractive indices of a number of tissues. Terahertz radiation is strongly absorbed in tissue so reflection imaging, which has lower penetration requirements than transmission, shows promise for dental or dermatological applications
Time dependent neutrino billiards
Quantum dynamica of a massless Dirac particle in time-dependent 1D box and
circular billiard with time-dependent radius is studied. An exact analytical
wave functions and eigenvalues are obtained for the case of linear
time-dependence of the boundary position
Berry phase for ferromagnet with fractional spin
We study the double exchange model on two lattice sites with one conduction
electron in the limit of an infinite Hund's interaction. While this simple
problem is exactly solvable, we present an approximate solution which is valid
in the limit of large core spins. This solution is obtained by integrating out
charge degrees of freedom. The effective action of two core spins obtained in
the result of such an integration resembles the action of two fractional spins.
We show that the action obtained via naive gradient expansion is inconsistent.
However, a ``non-perturbative'' treatment leads to an extra term in the
effective action which fixes this inconsistency. The obtained ``Berry phase
term'' is geometric in nature. It arises from a geometric constraint on a
target space imposed by an adiabatic approximation.Comment: 11 pages, 3 figures, revtex
Resonances and the thermonuclear reaction rate
We present an approximate analytic expression for thermonuclear reaction rate
of charged particles when the cross section contains a single narrow or wide
resonance described by a Breit-Wigner shape. The resulting expression is
uniformly valid as the effective energy and resonance energy coalesce. We use
our expressions to calculate the reaction rate for
C(p,)N.Comment: 4 pages, 1 figure, presented at the VIII International Conference on
Nucleus-Nucleus in Moscow (Russia) on June 17-21, 200
Complex numbers and symmetries in quantum mechanics, and a nonlinear superposition principle for Wigner functions
Complex numbers appear in the Hilbert space formulation of quantum mechanics,
but not in the formulation in phase space. Quantum symmetries are described by
complex, unitary or antiunitary operators defining ray representations in
Hilbert space, whereas in phase space they are described by real, true
representations. Equivalence of the formulations requires that the former
representations can be obtained from the latter and vice versa. Examples are
given. Equivalence of the two formulations also requires that complex
superpositions of state vectors can be described in the phase space
formulation, and it is shown that this leads to a nonlinear superposition
principle for orthogonal, pure-state Wigner functions. It is concluded that the
use of complex numbers in quantum mechanics can be regarded as a computational
device to simplify calculations, as in all other applications of mathematics to
physical phenomena.Comment: 14 pages. Latex_2e fil
Quantifying genetic differences between exported dairy bull calves and those sold for domestic beef production
peer-reviewedSelection bias is introduced when selection among individuals exists but the information used to inform that selection decision is not considered in downstream genetic evaluations. Genetic evaluations are undertaken in several countries for carcass-related metrics in prime cattle; no consideration is generally taken for animals that are harvested at a younger age for veal production and thus do not express the prime carcass phenotype. Although no veal industry exists in Ireland, dairy calves are routinely exported to continental Europe for veal production. The objective of the present study, based on a cross-sectional analysis of calf export data, was to determine quantitatively if genetic variability exists in whether purchased dairy-bred bull calves are immediately exported or retained within the country for domestic production. Also of interest was whether such a genetic difference was associated with differences in carcass weight, conformation score, and fat score in prime cattle relatives. Editing criteria were imposed to consider only Holstein-Friesian bull calves. Post-editing, the fate of 43,890 Holstein-Friesian bull calves (<100 d of age) was available; variance components for the binary phenotype (sold for export or not) were estimated using both linear and threshold animal models, and genetic correlations with carcass traits from 56,366 prime cattle were estimated. The heritability (standard error) of whether or not a calf was exported was 0.04 (0.01) on the linear scale and 0.07 (0.02) on the threshold scale. Although no explicit maternal genetic effect was detected, the proportion of the phenotypic variance due to maternal effects was 0.03 to 0.07. The genetic correlation (standard error) between the export phenotype with carcass weight, conformation score [scale 1 (poor) to 15 (excellent)], and fat score [scale 1 (thin) to 15 (fat)] in prime cattle was 0.002 (0.12), −0.25 (0.12), and −0.32 (0.11), respectively. The low heritability of the calf export phenotype and lack of a strong genetic correlation with carcass metrics suggest that other calf features might be greater determinants of the eventual fate of the calf. Accounting for the export phenotype in genetic evaluations of carcass traits in prime cattle had a negligible effect on the estimated breeding values for carcass merit
Decay of the Sinai Well in D dimensions
We study the decay law of the Sinai Well in dimensions and relate the
behavior of the decay law to internal distributions that characterize the
dynamics of the system. We show that the long time tail of the decay is
algebraic (), irrespective of the dimension .Comment: 14 pages, Figures available under request. Revtex. Submitted to Phys.
Rev. E.,e-mail: [email protected]
Choice of artificial insemination beef bulls used to mate with female dairy cattle
peer-reviewedUnderstanding the preferences of dairy cattle producers
when selecting beef bulls for mating can help
inform beef breeding programs as well as provide
default parameters in mating advice systems. The
objective of the present study was to characterize the
genetic merit of beef artificial insemination (AI) bulls
used in dairy herds, with particular reference to traits
associated with both calving performance and carcass
merit. The characteristics of the beef AI bulls used
were compared with those of the dairy AI bulls used on
the same farms. A total of 2,733,524 AI records from
928,437 females in 5,967 Irish dairy herds were used.
Sire predicted transmitting ability (PTA) values and
associated reliability values for calving performance
and carcass traits based on national genetic evaluations
from prior to the insemination were used. Fixed effects
models were used to relate both genetic merit and the
associated reliability of the dairy and beef bulls used on
the farm with herd size, the extent of Holstein-Friesian
× Jersey crossbreeding adopted by the herd, whether
the herd used a technician insemination service or do-ityourself,
and the parity of the female mated. The mean
direct calving difficulty PTA of the beef bulls used was
1.85 units higher than that of the dairy bulls but with
over 3 times greater variability in the beef bulls. This
1.85 units equates biologically to an expectation of 1.85
more dystocia events per 100 dairy cows mated in the
beef × dairy matings. The mean calving difficulty PTA
of the dairy AI bulls used reduced with increasing herd
size, whereas the mean calving difficulty PTA of the
beef AI bulls used increased as herd size increased from
75 cows or fewer to 155 cows; the largest herds (>155
cows) used notably easier-calving beef bulls, albeit the
calving difficulty PTA of the beef bulls was 3.33 units
versus 1.67 units for the dairy bulls used in these herds.
Although we found a general tendency for larger herds
to use dairy AI bulls with lower reliability, this trend
was not obvious in the beef AI bulls used. Irrespective
of whether dairy or beef AI bulls were considered, herds
that operated more extensive Holstein-Friesian × Jersey
crossbreeding (i.e., more than 50% crossbred cows)
used, on average, easier calving, shorter gestationlength
bulls with lighter expected progeny carcasses of
poorer conformation. Mean calving difficulty PTA of
dairy bulls used increased from 1.39 in heifers to 1.79
in first-parity cows and to 1.82 in second-parity cows,
remaining relatively constant thereafter. In contrast,
the mean calving difficulty PTA of the beef bulls used
increased consistently with cow parity. Results from
the present study demonstrate a clear difference in the
mean acceptable genetic merit of beef AI bulls relative
to dairy AI bulls but also indicates that these acceptable
limits vary by herd characteristics
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