2,544 research outputs found
Association between stall surface and some animal welfare measurements in freestall dairy herds using recycled manure solids for bedding
The objective of this cross-sectional study was to investigate the association between stall surface and some animal welfare measurements in upper Midwest US dairy operations using recycled manure solids as bedding material. The study included 34 dairy operations with herd sizes ranging from 130 to 3,700 lactating cows. Forty-five percent of the herds had mattresses and 55% had deep-bedded stalls. Farms were visited once between July and October 2009. At the time of visit, at least 50% of the cows in each lactating pen were scored for locomotion, hygiene, and hock lesions. On-farm herd records were collected for the entire year and used to investigate mortality, culling, milk production, and mastitis incidence. Stall surface was associated with lameness and hock lesion prevalence. Lameness prevalence (locomotion score ≥3 on a 1 to 5 scale) was lower in deep-bedded freestalls (14.4%) than freestalls with mattresses (19.8%). Severe lameness prevalence (locomotion score ≥4) was also lower for cows housed in deep-bedded freestalls (3.6%) than for cows housed in freestalls with mattresses (5.9%). In addition, the prevalence of hock lesions (hock lesion scores ≥2 on a 1 to 3 scale, with 1 = no lesion, 2 = hair loss or mild lesion, and 3 = swelling or severe lesion) and severe hock lesions (hock lesion score = 3) was lower in herds with deep-bedded freestalls (49.4%; 6.4%) than in herds with mattresses (67.3%; 13.2%). Herd turnover rates were not associated with stall surface; however, the percentage of removals due to voluntary (low milk production, disposition, and dairy) and involuntary (death, illness, injury, and reproductive) reasons was different between deep-bedded and mattress-based freestalls. Voluntary removals averaged 16% of all herd removals in deep-bedded herds, whereas in mattress herds, these removals were 8%. Other welfare measurements such as cow hygiene, mortality rate, mastitis incidence, and milk production were not associated with stall surface
Spectral determinants and zeta functions of Schr\"odinger operators on metric graphs
A derivation of the spectral determinant of the Schr\"odinger operator on a
metric graph is presented where the local matching conditions at the vertices
are of the general form classified according to the scheme of Kostrykin and
Schrader. To formulate the spectral determinant we first derive the spectral
zeta function of the Schr\"odinger operator using an appropriate secular
equation. The result obtained for the spectral determinant is along the lines
of the recent conjecture.Comment: 16 pages, 2 figure
Observation of mesoscopic crystalline structures in a two-dimensional Rydberg gas
The ability to control and tune interactions in ultracold atomic gases has
paved the way towards the realization of new phases of matter. Whereas
experiments have so far achieved a high degree of control over short-ranged
interactions, the realization of long-range interactions would open up a whole
new realm of many-body physics and has become a central focus of research.
Rydberg atoms are very well-suited to achieve this goal, as the van der Waals
forces between them are many orders of magnitude larger than for ground state
atoms. Consequently, the mere laser excitation of ultracold gases can cause
strongly correlated many-body states to emerge directly when atoms are
transferred to Rydberg states. A key example are quantum crystals, composed of
coherent superpositions of different spatially ordered configurations of
collective excitations. Here we report on the direct measurement of strong
correlations in a laser excited two-dimensional atomic Mott insulator using
high-resolution, in-situ Rydberg atom imaging. The observations reveal the
emergence of spatially ordered excitation patterns in the high-density
components of the prepared many-body state. They have random orientation, but
well defined geometry, forming mesoscopic crystals of collective excitations
delocalised throughout the gas. Our experiment demonstrates the potential of
Rydberg gases to realise exotic phases of matter, thereby laying the basis for
quantum simulations of long-range interacting quantum magnets.Comment: 10 pages, 7 figure
Light-cone-like spreading of correlations in a quantum many-body system
How fast can correlations spread in a quantum many-body system? Based on the
seminal work by Lieb and Robinson, it has recently been shown that several
interacting many-body systems exhibit an effective light cone that bounds the
propagation speed of correlations. The existence of such a "speed of light" has
profound implications for condensed matter physics and quantum information, but
has never been observed experimentally. Here we report on the time-resolved
detection of propagating correlations in an interacting quantum many-body
system. By quenching a one-dimensional quantum gas in an optical lattice, we
reveal how quasiparticle pairs transport correlations with a finite velocity
across the system, resulting in an effective light cone for the quantum
dynamics. Our results open important perspectives for understanding relaxation
of closed quantum systems far from equilibrium as well as for engineering
efficient quantum channels necessary for fast quantum computations.Comment: 7 pages, 5 figures, 2 table
Dielectric properties of Granodiorite partially saturated with water and its correlation to the detection of seismic electric signals
Transient electric signals emitted prior to earthquake occurrence are
recorded at certain sites in the Earth's crust termed sensitive. These field
observations enforce the laboratory investigation of the dielectric response of
rocks forming these localities. The dielectric relaxation of granodiorite rock
coming from such a sensitive locality (Keratea, Greece) reveals, through
complex impedance spectroscopy, that the activation volume for relaxation of
this rock is negative which so far has been reported only rarely. This result,
however, supports a theoretical model on the pre-seismic electric signals and
is likely to be correlated with the sensitivity of the site and hence with the
selectivity
Using Synchronic and Diachronic Relations for Summarizing Multiple Documents Describing Evolving Events
In this paper we present a fresh look at the problem of summarizing evolving
events from multiple sources. After a discussion concerning the nature of
evolving events we introduce a distinction between linearly and non-linearly
evolving events. We present then a general methodology for the automatic
creation of summaries from evolving events. At its heart lie the notions of
Synchronic and Diachronic cross-document Relations (SDRs), whose aim is the
identification of similarities and differences between sources, from a
synchronical and diachronical perspective. SDRs do not connect documents or
textual elements found therein, but structures one might call messages.
Applying this methodology will yield a set of messages and relations, SDRs,
connecting them, that is a graph which we call grid. We will show how such a
grid can be considered as the starting point of a Natural Language Generation
System. The methodology is evaluated in two case-studies, one for linearly
evolving events (descriptions of football matches) and another one for
non-linearly evolving events (terrorist incidents involving hostages). In both
cases we evaluate the results produced by our computational systems.Comment: 45 pages, 6 figures. To appear in the Journal of Intelligent
Information System
The Berry-Keating operator on L^2(\rz_>, x) and on compact quantum graphs with general self-adjoint realizations
The Berry-Keating operator H_{\mathrm{BK}}:=
-\ui\hbar(x\frac{
\phantom{x}}{
x}+{1/2}) [M. V. Berry and J. P. Keating,
SIAM Rev. 41 (1999) 236] governing the Schr\"odinger dynamics is discussed in
the Hilbert space L^2(\rz_>,
x) and on compact quantum graphs. It is
proved that the spectrum of defined on L^2(\rz_>,
x) is
purely continuous and thus this quantization of cannot yield
the hypothetical Hilbert-Polya operator possessing as eigenvalues the
nontrivial zeros of the Riemann zeta function. A complete classification of all
self-adjoint extensions of acting on compact quantum graphs
is given together with the corresponding secular equation in form of a
determinant whose zeros determine the discrete spectrum of .
In addition, an exact trace formula and the Weyl asymptotics of the eigenvalue
counting function are derived. Furthermore, we introduce the "squared"
Berry-Keating operator which is a special case of the
Black-Scholes operator used in financial theory of option pricing. Again, all
self-adjoint extensions, the corresponding secular equation, the trace formula
and the Weyl asymptotics are derived for on compact quantum
graphs. While the spectra of both and on
any compact quantum graph are discrete, their Weyl asymptotics demonstrate that
neither nor can yield as eigenvalues the
nontrivial Riemann zeros. Some simple examples are worked out in detail.Comment: 33p
Negative activation volume for dielectric relaxation in hydrated rocks
Negative defect activation volumes are extremely rare in solids. Here, we
report for the first time that this holds in a couple of hydrated rocks for
dielectric relaxation by exploring the complex impedance spectra at various
pressures and temperatures. The present findings mean that the relaxation time
of the relevant relaxation mechanisms decreases upon increasing pressure, thus
it may become too short at higher pressure and hence lead to the emission of
transient electric signals before fracture. This may constitute the
long-standing laboratory confirmation for the explanation of the generation of
electric signals prior to an earthquake, as recently pointed out by Uyeda et al
[Tectonophysics 470 (2009) 205-213]
Absence of sign problem in two-dimensional N=(2,2) super Yang-Mills on lattice
We show that N=(2,2) SU(N) super Yang-Mills theory on lattice does not have
sign problem in the continuum limit, that is, under the phase-quenched
simulation phase of the determinant localizes to 1 and hence the phase-quench
approximation becomes exact. Among several formulations, we study models by
Cohen-Kaplan-Katz-Unsal (CKKU) and by Sugino. We confirm that the sign problem
is absent in both models and that they converge to the identical continuum
limit without fine tuning. We provide a simple explanation why previous works
by other authors, which claim an existence of the sign problem, do not capture
the continuum physics.Comment: 27 pages, 24 figures; v2: comments and references added; v3: figures
on U(1) mass independence and references added, to appear in JHE
Isospin Character of the Pygmy Dipole Resonance in 124Sn
The pygmy dipole resonance has been studied in the proton-magic nucleus 124Sn
with the (a,a'g) coincidence method at E=136 MeV. The comparison with results
of photon-scattering experiments reveals a splitting into two components with
different structure: one group of states which is excited in (a,a'g) as well as
in (g,g') reactions and a group of states at higher energies which is only
excited in (g,g') reactions. Calculations with the self-consistent relativistic
quasiparticle time-blocking approximation and the quasiparticle phonon model
are in qualitative agreement with the experimental results and predict a
low-lying isoscalar component dominated by neutron-skin oscillations and a
higher-lying more isovector component on the tail of the giant dipole
resonance
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