2,756 research outputs found
Non-destructive classification and quality evaluation of proso millet cultivars using NIR hyperspectral imaging with machine learning
Millet is a small-seeded cereal crop with big potential and remarkable characteristics such as high drought resistance, short growing time, low water footprint, and the ability to grow in acidic soil. There is a need to develop nondestructive methods for differentiation and evaluation of the quality attributes of different of proso millet cultivars grown in the U.S. Current methods of cultivar classification are either subjective or destructive, time consuming, not allowing for the whole population to be tested, and requiring trained operators and special equipment. In this study, the feasibility of using near-infrared (NIR) hyperspectral imaging (900-1700 nm) to predict the quality attributes of proso millet (Panicum miliaceum L.) seeds as well to classify its different cultivars was demonstrated. Ten different cultivars of proso millet variety, which are the most popular in the US, investigated in this study included Cerise, Cope, Earlybird, Huntsman, Minco, Plateau, Rise, Snowbird, Sunrise, and Sunup. To reduce the large dimensionality of the hyperspectral imaging, principal component analysis (PCA) was applied, and the first two principal components were used as imaging features for building the classification models. The Classification performance showed a test accuracy rates as high as 99% for classifying the different cultivars of proso millet using gradient tree boosting ensemble machine learning algorithm. Moreover, using the partial least squares regression (PLSR) the coefficient of determination (R2) for quality prediction of proso millet seeds were 0.87, 0.80, 0.83, 0.93, and 0.92 for moisture content, crude protein, crude fat, ash, and carbohydrate, respectively. The overall results indicate that NIR hyperspectral imaging could be used to non-destructively classify and predict the quality of proso millet seeds
Giant slip lengths of a simple fluid at vibrating solid interfaces
It has been shown recently [PRL 102, 254503 (2009)] that in the plane-plane
configuration a mechanical resonator vibrating close to a rigid wall in a
simple fluid can be overdamped to a frozen regime. Here, by solving
analytically the Navier Stokes equations with partial slip boundary conditions
at the solid fluid interface, we develop a theoretical approach justifying and
extending these earlier findings. We show in particular that in the perfect
slip regime the above mentioned results are, in the plane-plane configuration,
very general and robust with respect to lever geometry considerations. We
compare the results with those obtained previously for the sphere moving
perpendicularly and close to a plane in a simple fluid and discuss in more
details the differences concerning the dependence of the friction forces with
the gap distance separating the moving object (i.e., plane or sphere) from the
fixed plane. Finally, we show that the submicron fluidic effect reported in the
reference above, and discussed further in the present work, can have dramatic
implications in the design of nano-electromechanical systems (NEMS).Comment: submitted to PRE (see also PRL 102, 254503 (2009)
Contribution of Bremsstrahlung Emission from Lyman-alpha Clouds to the Microwave Background Fluctuations
I calculate the contribution of Bremsstrahlung emission from Lyman-alpha
absorption clouds to the brightness of the microwave sky. The calculation is
based only on the assumption that the clouds below the Lyman-limit are in
photoionization equilibrium with a UV background radiation, and avoids any
uncertainty about the clumpiness of the gas. I predict a minimum fluctuation
amplitude in the Rayleigh-Jeans regime of DeltaT/T =
10^{-5.5+-0.4}*J_21*(L/5cm)^2, which varies over characteristic angular scales
of 1-100'', where L is the observed wavelength and J_21 is a weighted redshift
average of the UV background intensity at the Lyman-limit in units of 10^{-21}
erg cm^{-2} s^{-1} Hz^{-1} sr^{-1}. Detection of this signal can be used to map
the intergalactic hydrogen distribution and to calibrate the UV background at
high redshifts. Existing VLA observations constrain J_21<10^{1.3+-0.4}, unless
some of the extended flat-spectrum sources which were detected are Lyman-alpha
absorption systems.Comment: 9 pages, uuencoded compressed Postscript, no figure
Gravitational Lensing of the X-Ray Background by Clusters of Galaxies
Gravitational lensing by clusters of galaxies affects the cosmic X-ray
background (XRB) by altering the observed density and flux distribution of
background X-ray sources. At faint detection flux thresholds, the resolved
X-ray sources appear brighter and diluted, while the unresolved component of
the XRB appears dimmer and more anisotropic, due to lensing. The diffuse X-ray
intensity in the outer halos of clusters might be lower than the sky-averaged
XRB, after the subtraction of resolved sources. Detection of the lensing signal
with a wide-field X-ray telescope could probe the mass distribution of a
cluster out to its virialization boundary. In particular, we show that the
lensing signature imprinted on the resolved component of the XRB by the cluster
A1689, should be difficult but possible to detect out to 8' at the 2-4 sigma
level, after 10^6 seconds of observation with the forthcoming AXAF satellite.
The lensing signal is fairly insensitive to the lens redshift in the range
0.1<z<0.6. The amplitude of the lensing signal is however sensitive to the
faint end slope of the number-flux relation for unresolved X-ray sources, and
can thus help constrain models of the XRB. A search for X-ray arcs or arclets
could identify the fraction of all faint sources which originate from extended
emission of distant galaxies. The probability for a 3 sigma detection of an
arclet which is stretched by a factor of about 3 after a 10^6 seconds
observation of A1689 with AXAF, is roughly comparable to the fraction of all
background X-ray sources that have an intrinsic size of order 1''.Comment: 41 LaTeX pages, 11 postscript figures, 1 table, in AASTeX v4.0
format. To appear in ApJ, April 1, 1997, Vol. 47
An Observational Test for the Anthropic Origin of the Cosmological Constant
The existence of multiple regions of space beyond the observable Universe
(within the so-called "multiverse") where the vacuum energy density takes
different values, has been postulated as an explanation for the low non-zero
value observed for it in our Universe. It is often argued that our existence
pre-selects regions where the cosmological constant is sufficiently small to
allow galaxies like the Milky Way to form and intelligent life to emerge. Here
we propose a simple empirical test for this anthropic argument within the
boundaries of the observable Universe. We make use of the fact that dwarf
galaxies formed in our Universe at redshifts as high as z~10 when the mean
matter density was larger by a factor of ~10^3 than today. Existing technology
enables to check whether planets form in nearby dwarf galaxies and globular
clusters by searching for microlensing or transit events of background stars.
The oldest of these nearby systems may have formed at z~10. If planets are as
common per stellar mass in these descendents as they are in the Milky Way
galaxy, then the anthropic argument would be weakened considerably since
planets could have formed in our Universe even if the cosmological constant was
three orders of magnitude larger than observed. For a flat probability
distribution, this would imply that the probability for us to reside in a
region where the cosmological constant obtains its observed value is lower than
\~10^{-3}. A precise version of the anthropic argument could then be ruled-out
at a confidence level of ~99.9%, which constitutes a satisfactory measure of a
good experimental test.Comment: JCAP, in pres
Finite-size effects on multibody neutrino exchange
The effect of multibody massless neutrino exchanges between neutrons inside a
finite-size neutron star is studied. We use an effective Lagrangian, which
incorporates the effect of the neutrons on the neutrinos. Following Schwinger,
it is shown that the total interaction energy density is computed by comparing
the zero point energy of the neutrino sea with and without the star. It has
already been shown that in an infinite-size star the total energy due to
neutrino exchange vanishes exactly. The opposite claim that massless neutrino
exchange would produce a huge energy is due to an improper summation of an
infrared-divergent quantity. The same vanishing of the total energy has been
proved exactly in the case of a finite star in a one-dimensional toy model.
Here we study the three-dimensional case. We first consider the effect of a
sharp star border, assumed to be a plane. We find that there is a non-
vanishing of the zero point energy density difference between the inside and
the outside due to the refraction index at the border and the consequent
non-penetrating waves. An analytical and numerical calculation for the case of
a spherical star with a sharp border confirms that the preceding border effect
is the dominant one. The total result is shown to be infrared-safe, thus
confirming that there is no need to assume a neutrino mass. The ultraviolet
cut-offs, which correspond in some sense to the matching of the effective
theory with the exact one, are discussed. Finally the energy due to long
distance neutrino exchange is of the order of , i.e. negligible with respect to the neutron mass density.Comment: Latex file (Revtex), 34 pages, 8 postscripted figure
Intergalactic Magnetic Fields from Quasar Outflows
Outflows from quasars inevitably pollute the intergalactic medium (IGM) with
magnetic fields. The short-lived activity of a quasar leaves behind an
expanding magnetized bubble in the IGM. We model the expansion of the remnant
quasar bubbles and calculate their distribution as a function of size and
magnetic field strength at different redshifts. We generically find that by a
redshift z=3, about 5-20% of the IGM volume is filled by magnetic fields with
an energy density >10% of the mean thermal energy density of a photo-ionized
IGM (at T=10^4 K). As massive galaxies and X-ray clusters condense out of the
magnetized IGM, the adiabatic compression of the magnetic field could result in
the field strength observed in these systems without a need for further dynamo
amplification. The intergalactic magnetic field could also provide a nonthermal
contribution to the pressure of the photo-ionized gas that may account for the
claimed discrepancy between the simulated and observed Doppler width
distributions of the Ly-alpha forest.Comment: 40 pages, 8 figures, submitted to Ap
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